Starting Hardmode is very difficult: you’re underequipped and almost everything is stronger than you. You will have to return underground in search of ores to get some decent gear. But first, you’ll need to make a detour because none of that new ore actually exists yet. You’ll have to smash a few Altars with the Pwnhammer to make it appear. Every time you destroy an Altar, ore will be generated in various places underground, spawning more densely at lower depths.
The pattern will repeat with additional altars destroyed, spawning more Cobalt or Palladium, then more Mythril or Orichalcum, then more Adamantite or Titanium. There's diminishing returns on this: after you've smashed your first three altars, generating that amount of ore again requires you to smash a further nine (12 total), then 21 (33 total).
Also note, however, that each altar destroyed may spawn a new block of Ebon/Crimstone, or Pearlstone somewhere in the world, causing the respective biomes to spread from another location.
Natural deserts typically don't last long in hardmode. When corrupted, crimsoned, or hallowed, they become very similar to their respective biomes. Hardmode deserts are the only places where the Mummy can be found.
The Hallow spreads rapidly through the world, just like the Corruption and Crimson. Be wary of the seemingly whimsical denizens of the Hallow. All of them are hostile and are just as dangerous as their corrupted counterparts. Like with the evil biomes, players new to Hardmode should avoid staying in this biome for longer than necessary.
Crimson spreads identically to Corruption, and is just as dangerous, or perhaps even worse, since the Herpling, which has no corrupt counterpart, exists. They are very fast, have a short hitbox, high health, defense, and high damage. Their only significant weakness is rough terrain, as they will have difficulty reaching the high speeds they often use to surprise players. Extra caution is advised, especially in flat terrain.
Mining Hardmode Ores
Once enough ore has been spawned, the player should begin mining Cobalt or Palladium with a Molten Pickaxe. The other ores cannot be mined. Proceed with extreme caution: the most dangerous biomes in Hardmode are found underground. If the player created a Hellevator, they should use it to access the lower layers quickly. Hardmode ores are more abundant deeper underground.
This previously trivial biome has had its difficulty increased significantly. Hardmode ores are not very common in this layer. It is best to pass through to lower layers, the best location being right above the underworld and below the lava layer of the Caverns.
This biome is very dangerous, but it is less dangerous than the Underground Corruption, Crimson, and Hallow. It's for this reason that this biome is one of the ideal biomes for mining hardmode ores. However, don't underestimate the new monsters in this biome: the Armored Skeleton's "Broken Armor" debuff is particularly lethal. Consider returning to town and talking to the Nurse if hit by the debuff. They sometimes drop Armor Polish, which prevents the debuff and will be very helpful later on. The Mimic will also spawn underground here, and if you can, attempt to take some down. You can use the Lifeform Analyzer to tell when these enemies are near. Be wary, however, that even they will inflict high amounts of damage, so ranged and/or high knockback weapons are recommended.
It is recommended to mine elsewhere until Mythril armor or better is obtained. Chaos Elementals and Enchanted Swords can easily reach the player. If you do decide to venture in and run into a Hallowed Mimic in chest form, avoid going near, and especially avoid attacking it. If one is already on your tail, you should attempt to use your Magic Mirror at the nearest convenience.
As with the Underground Hallow, it is recommended that the player avoids this biome until they obtain Mythril armor. The denizens of this biome will make mining extremely difficult for a player without hardmode gear.
Similarly the underground Corruption and Hallow, the Crimson should be avoided early on in hardmode. Attempt to stay farther from this biome than others, though, as Floaty Grosses can pass through blocks, even if you aren't in the biome.
The player can find Truffle Worms in this biome, which are used to summon Duke Fishron. Otherwise, the new enemies are comparable to those of other underground biomes, and their attacks, especially those of the Giant Fungi Bulb, can be very dangerous. If you are exposed to the biome directly, you may be hit by the Fungi Bulb's attacks, which are very small but deal a lot of damage. Stay away from this biome unless you need an emergency supply of Glowing Mushrooms or Mushroom Seeds.
It can be very difficult to survive long enough in Hardmode biomes to mine enough ore. If the player finds they are having difficulty mining, they should consider looking for ores in the ceiling of the Underworld. This biome has the same mobs as it did pre-Hardmode, making it considerably safer than almost anywhere else in the world.
Aim to upgrade to a Cobalt Drill or Palladium Drill (or their pickaxe equivalents) as quickly as possible. The Cobalt Drill or Pickaxe and its counterpart can mine Mythril/Orichalcum. The first Mythril/Orichalcum ores mined should be used to craft a Mythril/Orichalcum Anvil and then a Mythril Drill (or their Orichalcum counterparts). The Mythril Drill and Pickaxe (and their Orichalcum counterparts) can mine Adamantite/Titanium. The first 30 Adamantite/Titanium ore mined should be used to create an Adamantite Forge or Titanium Forge. Upgrading to an Adamantite Drill or Titanium Drill isn't crucial, as it does not grant access to any new ores.
Be mindful when opening chests. A seemingly innocuous treasure chest may be a Mimic posing as a chest. Mimics will chase the player when they approach or when attacked. A good approach is to shoot any chests with a ranged weapon before opening them. This will cause any Mimics to break their ruse and attack. Mimics can drop items that are incredibly useful in hardmode, and also always drop several gold coins.
Use any leftover ore to upgrade armor, then weapons, and lastly tools. Keep mining until enough Adamantite or Titanium is collected to craft a full set of armor and any weapons or tools the player may want.
This time, it's much more difficult with the new Goblin Summoner in the mix. She can attack you with her highly damaging spells. However, it is indeed worth the trouble to defeat her, as she can drop powerful weapons, like the Shadowflame Bow, which can prove devastating when used against the mechanical bosses, as these weapons can inflict the Shadowflame debuff, dealing 5 damage per second.
A Pirate Invasion can occur after a player smashes one demon altar, or alternatively when the player uses a Pirate Map.
The Pirate Invasion can generally be difficult in early Hardmode, so it is best if the player is prepared in case one arrives. When a Pirate Invasion spawns or is summoned using a Pirate Map, a message will appear saying "Pirates are approaching from the (East/West)!"
When the Pirates' initial wave reaches the spawn, their arrival is announced with "The Pirates have arrived!"
Whilst you're trying to find enough ore to make better gear, it's highly recommended that you make the following other preparations in the run-up to the mech bosses:
Make sure you have a home for the Wizard. Like the Goblin Tinkerer and Stylist, he can be found tied up underground. This NPC is mandatory for magic users, as he sells Greater Mana Potions and crafting ingredients used to craft some very powerful spells.
Make sure you have a full set of buff potions and at least a stack of Greater Healing Potions or Honeyfin. The mech bosses' damaging attacks will eat away at your health very quickly, so acquiring better potions is recommended.
Collecting souls is the last task the player should complete before fighting the Mechanical bosses. There are three types of souls dropped by normal monsters: Soul of Light, Soul of Night, and Soul of Flight. Souls of Light can be obtained from any monster found in the Underground Hallow, Souls of Night can be obtained from any monster found in the Underground Corruption or Crimson, and lastly, Souls of Flight can be obtained from Wyverns. The order in which the player obtains these souls does not matter. However, it can be advantageous to gather Souls of Flight first, as Wings are very useful when navigating the Underground Hallow or Underground Corruption.
Soul of Flight
Wyverns can be found at very high altitudes, at around the same level as Floating Islands. Look for Wyverns on Floating Islands, as it is much easier to fight them this way.
The only hardmode addition to floating islands is the Wyvern enemy. These Wyverns are of interest because they drop Souls of Flight, which are required to craft wings.
Wyverns are very difficult to kill. They fly through the air using the same AI as worms, but they move much faster, do much more damage, and have a lot more life. They are very difficult to dodge and attack at the same time. Piercing weapons are very effective against the Wyvern, like with all segmented monsters.
Souls of Light can be found by killing enemies in the Underground Hallow. Underworld Enemies spawned below the Underground Hallow will also drop Souls. Try to gather crystal shards while looking for souls. Try to gather at least 50 souls, although more is better. If the Hallow in your world went through a Spider Cave, you can also farm the spiders, taking advantage of their fast spawn rate.
Biome Keys have an extremely rare drop from enemies in the six main biomes (Hallow, Corruption, Crimson, Jungle, Desert, and Snow). These can be used to open the Biome Chests in the Dungeon once that Plantera has been defeated (see below), which contain extremely powerful items.
Fifteen Souls of Light or Night can be used to make Light or Night Keys, respectively. A Key of Light or Night placed into an empty chest will create Hallowed or Corrupt/Crimson Mimics, which are larger than normal mimics and more dangerous, but with unique rewards.
Hallowed, Corrupt and Crimson Mimics can also naturally appear in their respective underground biomes.
Like King Slime, much of the reason she is easier than the 3 main bosses at this point is because of her limited movement and attacking capabilities; she has no rapid, long range attack, and even in her second form she moves significantly slower than The Twins or Skeletron Prime.
The Three Mechanical Bosses
Once you have a stockpile of the various hardmode resources, it's time to begin preparing to defeat the first three hardmode bosses. Each must be summoned with an item that can be crafted or dropped by enemies. It's also possible for one to spawn on its own at sunset, though the player will probably not be able to defeat it unless they are well prepared.
Recommended Equipment for Mechanical Bosses
Following is a list of equipment recommendations for use against the mechanical bosses. This is not an exhaustive list; other items may prove to be effective. This list assumes no Hardmode bosses have been defeated yet: This content is transcluded from Guide:Class setups.
At this point, you may also want to start working on getting good modifiers for your equipment.
Proper terrain preparation is almost completely essential to successfully defeat all three mechanical bosses. Players who intend to solo the hardmode bosses will find the task very challenging without an adequate arena.
For solo players, build a very long bridge out of wood platforms. The bridge should be at least 1000 platforms long, but 2500 is recommended. Build the bridge a large distance from the ground; the ground should not be visible from any part of the bridge. Place blocks at each end of the bridge to prevent running off of the sides.
For team players, the arena can be much shorter. A team arena can be between 250-500 platforms long, but should also have 2-3 separate rows. Space the rows so they are not too close together, but are reachable with rocket boots.
Another Re-Usable Arena can be made out of the pre-hardmode boss arena, the old ones army one, and your skybridge. This allows reusing of the old arenas for Eye of Cthulhu/King Slime, events, and the wyvern arena.
If you don't quite feel up to the task of making a second very long bridge, you could simply use the first one you built for the Wall of Flesh. This will also make the first fight easier due to all of the ambient light. However, after defeating your first mechanical boss, this becomes much harder due to the additional spawns of Lava Bats and Red Devils.
Fighting the Mechanical Bosses
The Destroyer is arguably the easiest of the three bosses and should be fought first. The Destroyer has a chance of spawning naturally at sunset with the message "You feel vibrations deep below..." It can also be summoned by using a Mechanical Worm at night. Fight the Destroyer first if you prefer melee or ranged, as its souls can be used to craft Light Discs and Megashark.
Recommended Equipment: See above section "Recommended Equipment for Hardmode Bosses"
The Destroyer is the hardmode version of Eater of Worlds. The Destroyer uses a variation of worm AI, burrowing into the ground and making long sweeping passes at the player. The Destroyer is much longer than the Eater of Worlds and moves much faster. Unlike the Eater of Worlds, the Destroyer does not break into segments. The Destroyer's segments all have a shared life of 80000. All of its segments will be destroyed when this life reaches 0. The Destroyer will release Probes as it takes damage. Probes will drop hearts when killed. If the Destroyer is not defeated before 4:30 AM, it will run away.
Piercing weapons and AoE weapons are particularly effective against this boss. The Destroyer will frequently try to trap you with its body. Use a hook to get out of these situations. The Destroyer's drops come from its head when it is killed. When its health is very low, wait until any of its segments are above the ground before finishing it off.
The destroyer does not despawn if you use a Magic Mirror or Recall Potion to flee and will instead follow you. This can be helpful if the player sets up a house near the spawn point for the Nurse to move in, aiding the player in healing if the player's health is low.
As of 1.2, hallowed equipment (except for the Drax/Pickaxe Axe, which is necessary for progression) doesn't require boss souls; it only requires Hallowed Bars, which you can farm up from the Destroyer.
It is recommended to fight Skeletron Prime next, as ranged characters can make a Flamethrower if he is defeated.
Recommended Equipment: See above section "Recommended Equipment for Hardmode Bosses"
Skeletron Prime is the hardmode version of Skeletron. Skeletron Prime behaves very similarly to its predecessor. It alternates between attacking with its various appendages and using a deadly spinning attack with its head. Skeletron Prime has a lot of health and can take a long time to kill. If Skeletron Prime is not defeated before the sun rises, it will use an attack that instantly kills the player on touch.
The damage from all of its arms can add up quickly. Try to destroy the arms before focusing on the head. The Prime Saw and Prime Vice are very difficult to avoid and should be destroyed first. The Prime Laser is only a medium threat and should be killed after the Vice and Saw, and the Prime Cannon can be ignored. There are two methods to avoiding Skeletron Prime's attacks. The first is to use the maximum speed of Lightning or Frostspark Boots to stay out of reach (Prime Saw will always be able to keep up), combined with well-timed jumps to throw off the aim of Skeletron Prime's spinning head attack. The second method is to use Gravitation potions for a similar effect, though it can be harder to dodge some of Skeletron Prime's attacks this way.
The last of the three mechanical bosses is the Twins. This boss is the hardest of the three for most players and should be defeated last. The Twins have a chance of spawning at sunset with the message "This is going to be a terrible night..." They can also be summoned by using a Mechanical Eye at night. The Twins are recommended for magic and summoning players, as the Rainbow Rod, Magical Harp, and Optic Staff will be very useful weapons later on.
Recommended Equipment: See above section "Recommended Equipment for Hardmode Bosses"
The Twins are the hardmode version of Eye of Cthulhu. Both Twins will alternate between their signature attack (Laser for Retinazer, Cursed flame for Spazmatism), and charging at the player. The two choose attacks independently of the other. There will be times when one uses their signature while the other charges, when they both use their signature, and when they both charge. When a Twin gets down a certain amount of health (8000 / 12000 for Retinazer, 9200 / 13800 for Spazmatism), it will transform into a more powerful second stage. Both will gain a rapid-fire version of their signature attack and a much more damaging melee attack in their second stages. The first Twin killed will not yield any drops. When the second Twin is killed, the listed drops will appear where it was killed. The eyes can be killed in any order. If the Twins are not defeated before the sun rises, they will run away.
Each twin is much more dangerous in its second stage. Focus on one Twin at a time, and only move on to the second Twin when the first is destroyed. Retinazer's stage one signature is less dangerous, so kill Spazmatism first. The Twins have a charging attack that is extremely difficult to dodge. This charging attack will cripple a player if they can't consistently dodge it. There are two methods to dodging the attacks, like with Skeletron Prime. The first method is to reach max running speed with Lightning or Frostspark Boots and use timed jumps to throw off the trajectory of the charge. Jump just as a Twin is about to start a charge while maintaining run speed. This will cause the charging Twin to charge too fast, and then attempt to correct it as they try to charge again. The second method is to use Gravitation Potions and constantly fall - they won't be able to catch up to you. If a Twin is off screen too long, it will despawn like any other enemy (only on console and mobile though). This can be used to make Spazmatism despawn and simplify the fight greatly. However, you will not gain the loot.
Once any mechanical boss has been defeated, new challenges unlock, and the player gains access to new materials to work with, starting with the souls and bars dropped by the boss. Hallowed Bars can be used to craft Hallowed armor and several kinds of weapons.
The player can also return to the Underground Jungle to search for Life Fruit, a consumable item that can increase the player's maximum health to 500.
Solar eclipses occur randomly at dawn and last throughout the day. The enemies here are extremely dangerous and it may require gear from the Hardmode Jungle and Dungeon to efficiently farm them. The Death Sickle is good for melee characters with its high DPS and piercing ability. Sword users should also take special note of the Broken Hero Sword that has a chance to drop from Mothron, a rare monster that can challenge newer players -- one can create the True Excalibur or True Night's Edge and then craft a Terra Blade. The Possessed, Fritz, and Creature From the Deep are exclusive to the Desktop version, Console version, and Mobile version, making the Solar Eclipse much harder there. After defeating Plantera, Nailheads, Butchers, and Psychos begin to appear, making even the most well-equipped player thus far to reach for his Magic Mirror.
Two new enemies now spawn in the Underworld after one Mechanical Boss has been defeated. Lava Bats are simply a stronger version of the Hellbat. Red Devils are the real danger, being able to deal over 100 damage with their trident attack. It's recommended that the player does anything they need to do in the Underworld (such as farming the Wall of Flesh for its special drops) before defeating mechanical bosses; otherwise, doing anything here may become much harder. As soon as Hardmode begins, it is possible to find a Tortured Soul which, when purification powder is used in it rather than killing it, transformed into a Tax Collector, which greatly boosts income.
Now that one or more of the mechanical bosses have been defeated, Chlorophyte ore spawns throughout the underground jungle. Hardmode also makes it so that Life Fruits can occasionally be found growing amongst the foliage. Harvesting these two items should be a top priority. Life Fruits increase the player's health by 5, up to a maximum of 500, and Chlorophyte can be crafted into weapons and armor a step above Hallowed equipment.
Players using melee or ranged weapons can make even better armor by acquiring an additional material. Creating a house in the glowing mushroom biome will spawn the Truffle NPC, who sells the Autohammer. The Autohammer turns Chlorophyte bars into Shroomite bars, which are used to create Shroomite armor, a great armor for ranged attackers. Giant Tortoise drop Turtle Shell, which when combined with Chlorophyte Bars make Turtle armor, a powerful melee armor set. Make note that the Autohammer cannot be purchased until Plantera has been defeated.
Plantera can be one of the easiest bosses if you have an arena. Simply bomb out a large cave (although of course, make sure NOT to accidentally destroy Plantera's Bulb) and put a short wall in the middle of the cave. Put platforms below the wall so that you have a place to grapple to, and summon Plantera. Run around the wall you built and you should be fine. (See also: Guide:Plantera strategies)
Upon defeating Plantera, the message "Screams are echoing from the dungeon..." appears, and powerful new enemies are added to the dungeon. The boss also drops the Temple Key, which is used to open the Jungle Temple.
After defeating Plantera, you will pick up a Temple Key that is used to unlock the door to the Jungle (also known as the Lihzahrd Temple). It is small compared to the normal dungeon, but it contains far more traps. In the console version of Terraria, you can use two Teleporters to teleport into the temple.
Golem in its first stage is made significantly easier if the player focuses on destroying his fists before releasing his head's other attacks. Constant damage to the fists will nullify their attacks, leaving you free to attack at a range while avoiding his head's fireballs and lasers. In his second form, it is best to have built platforms to run underneath his jumping body Bowser-style while taking shots at him and avoiding his head attacks. This means that ranged attacks would be the safest strategy to beating him, providing you don't make too many mistakes and other mobs don't interfere. Note that his body has the ability to move midair, meaning that he can still change direction and land on you after running beneath him at a close distance.
After defeating Plantera, the dungeon's difficulty increases dramatically. There are stronger enemies and new drops from each. Also, note that the dungeon has 5 biome-related chests. To unlock each one, you may need to defeat many of the respective biome's enemies to get a key, which is used to unlock the respective chest. Dungeon Spirits, which may spawn after the player kills enemies in the dungeon, drop Ectoplasm, which is used to craft Spectre armor, a great armor for mages.
Recommended Buff Potions (all classes): Ironskin, Regeneration, Swiftness, Thorns, Water Walking, Well Fed, Wrath, Rage, Lifeforce, Endurance, Summoning, Gravitation (optional)
Duke Fishron is one of the hardest bosses in the game as of 220.127.116.11. Just summoning the Duke is a significant challenge in itself, as you will need to capture the wily and elusive Truffle Worm. The spawn rates in naturally occurring Underground Glowing Mushroom biomes are low, and if you intend on getting the Fishron Wings (1/15 chance), as well as all his drops, you’ll need to defeat him on average 10 times. Add in a few more for the times you die and because the RNG hates you, and you could easily be looking at 20-25 truffle worms needed. Trying to net that many manually, even with the help of a Clentaminator, Golden Bug Net and Blue Solution, is tedious and frankly boring. Your best bet is to build a Truffle Worm farm, for which you can find a guide here.
Once you’ve collected sufficient Truffle Worms, you should select your class. Melee, ranged, and magic are all viable options. Ironically, the ranger, which has up until now been a mainstay of boss fights, is probably the worst option. Although the Ranger is still great at dealing high DPS, the lack of a self-healing attack, unlike the other two, also makes this the most dangerous approach, and with the Duke’s extremely high damage, leaves you very little margin for error. If you're a ranger, make one mistake and you’re dead. Melee using Vampire Knives is the second option, which is relatively safe. And despite Spectre armor (Hood) getting its damage nerfed by 40%, and mana potions nerfed a further 25%, the magic approach is probably still the best one (which goes to show how overpowered it was). As of 1.3, the new magic weapon Life Drain, with a 20% drop rate from the difficult Crimson Mimic, can serve as a magical replacement for the Vampire Knives, and can be obtained earlier in Hardmode by farming for Souls of Night, crafting a Key of Night, and farming Crimson Mimics. However, know that whereas the Vampire Knives' regenerative powers are proportional to damage, Life Drain simply provides faster regeneration, which may not be enough to save the player from death.
Unlike most boss fights, an arena is of little help. Duke Fishron seems to have been designed with the intention of being farm-proof (he’s not), and if you sit still or linger in the same area, he can literally take you from a full 600hp to zero in two seconds flat in his second stage, whereas if you keep moving and keep your distance, you shouldn’t take much damage. It is important to keep in mind that if you move too far away from him that he will despawn, wasting a precious Truffle worm.
Once you’re ready to fight the Duke, summon him by fishing in the Ocean using a Truffle Worm as bait. From there, the best strategy is to just continually run away while firing until he’s dead. Don’t stop moving at any time or you’ll die. In theory it’s best to use a Gravitation Potion for maximum mobility, but in reality you may actually have very little experience using Gravitation Potions, as they can be disorienting, you can run into floating islands, mountains, or worst, lakes (which will kill you), you can’t fly too high or you will float, and it will be very difficult to dodge (which will kill you). With Wings and Frostspark Boots, you’re very mobile on the ground too and both approaches are viable, so go with what you’re most comfortable with. The Tabi/Master Ninja Gear will allow you to dash out of the way of his more lethal attacks, but be wary of accidentally dashing into a Sharknado. If you have the Shield of Cthulhu, you are even better off, as it allows to dash into him without taking damage (if timed correctly). This can actually be a reliable lifesaver from his quick lunging attacks during his second stage, especially on expert mode (3rd stage). Note that of 1.3 if the player leaves the Ocean Biome Duke Fishron's defense and attack will double, making fighting across the map an invalid option. The best option as of the latest update will be to build platforms over the Ocean Biome and begin building a flexible arena.
Although Duke Fishron is a very difficult boss, he’s probably still easier than the Lunar Events and it’s probably best to beat him before taking on the Events. However, if you find yourself stuck attempting and failing to kill him, the Lunar Events may be the only other option to continue. If you do undergo the events, it's best to defeat your class's pillar (Vortex for ranged, Nebula for magic, Solar for melee, and Stardust for Summoner). Defeating a Pillar once allows the crafting of one of the Lunar Weapons. An optional detour is to defeat the Stardust Pillar to gain a powerful minion (Stardust Dragon or Stardust Cell) to aid you in the fight. BEWARE: if you defeat all Lunar Pillars, the Moon Lord will spawn, and chances are if you can't defeat Fishron, you have an even lower chance of defeating the Moon Lord. If you’re fighting Duke Fishron multiple times, the fight will be somewhat easier once you've acquired his weapon drops and wings.
The Pumpkin Moon is summoned at night using the Pumpkin Moon Medallion. Unlike the Blood Moon and Solar Eclipse, enemies appear in up to 15 consecutive waves, similar to an invasion. During this event, the moon turns orange with a jack 'o lantern face.
The Frost Moon is summoned at night using the Naughty Present. It is one of the most difficult events in the game, as it is meant for endgame players. Like the Pumpkin Moon, enemies appear in 15 standard waves as well as 5 extra bonus waves. During this event, the moon changes color to look like the face of a snowman.
Martian Madness is an invasion-type event that can happen after defeating Golem. Occasionally, in the outer two-thirds of your map, a Martian Probe will randomly appear. If it scans you and escapes, the event will start. This event cannot be triggered manually.
After cycling through its attacks a few times, it will fade away, and reappear in a ritual-like circle, with duplicates of itself called Ancient Cultists. The player must hit the real cultist to stop the ritual. Attacking a fake or letting the ritual finish will cause a Phantasm Dragon to spawn, and cause the respective Ancient Cultist to fight alongside the real cultist, if the former happens. This fake cultist can be destroyed by attacking the real cultist when it performs its ritual again.
Attacking a fake while the Phantasm Dragon is still alive will result an Ancient Vision being spawned, NOT another Phantasm Dragon.
Once the Lunatic Cultist is defeated, four pillars will spawn in the world. These can easily be found with the map. Be sure to pick up the Ancient Manipulator the Cultist drops, as it is needed to craft end-game gear.
Chances are that you will be near a pillar when they spawn. The pillars represent the four classes: Solar for melee, Vortex for ranged, Nebula for magic, and Stardust for summoning. There is no set order necessary to kill them, but it is preferable to take on the one corresponding to your class first, then the Stardust Pillar to get the powerful Stardust Dragon Staff.
The Solar Pillar is a tough one to crack, and, like all the Pillars, you will be under constant attack from its minions.
To make the Solar Pillar (or any pillar) vulnerable, you must kill 100 (150 on Expert) of its minions to deactivate its shield, allowing it to be harmed directly.
Try to stay out of the air around the Solar Pillar if possible, because the Crawltipedes will swarm and kill you quickly otherwise. If need be, aim at their weak spot, the tail, to kill them. This will give you a small window to take flight before another spawns.
Be sure to also be wary of the Corites that spawn as well, because their charge attack can be deadly, or even fatal when they swarm you.
The Selenians are extremely deadly when they are spinning, as they can reflect damage, which is able to deal heavy damage to the caster/shooter. Avoid high damage ranged/magic weapons like Nebula Blaze and Sniper Rifle. It is recommended to use low-damage, high fire weapons like the Razorpine, melee weapons, and summons.
Because many of the enemies from this pillar cannot pass through solid blocks, it's recommended that you attempt to find an area where most mobs will have trouble reaching you, but where you can reach them. If possible, try to obtain a weapon that can pass through walls, such as the Nettle Burst or Flying Dragon.
Like every Pillar, to make the Vortex Pillar susceptible to damage, you must defeat 100 (150 on Expert) minions to deactivate its shield.
Try to take out the Storm Divers and Alien Queens first, as the Storm divers have a very strong shotgun attack that can deal large amounts of damage, while the Alien Queens can inflict the distorted debuff, which leaves the player extremely susceptible to other enemies.
Gravity is distorted around areas of the Vortex Pillar as well, so beware of the area around it. Because this is a ranged pillar, you will find that many of the enemies are going to fire volleys of projectiles at you. Due to this, it is recommended you have a Black Belt or a Master Ninja Gear, so you can have a slight chance to dodge these attacks.
Like every Pillar, to make the Nebula Pillar susceptible to damage, you must defeat 100 (150 on Expert) minions to deactivate its shield.
Focus on the Brain Sucklers that fly at you to prevent them from latching onto your head. If they do, aim your weapon above you to knock them off, or simply swing any regular sword/ melee weapon. The Nebula Floaters are tricky, as they will randomly teleport around. Take them out quickly, and dodge their beam attacks.
With this pillar, it is best to avoid the ground. Predictors and Evolution Beasts can make quick work of any player ground-bound, so sticking to the air is best. This is because Brain Sucklers have no projectile attack, and are relatively easy to kill. If the player is skilled, the pillar can be defeated relatively easily.
Like every Pillar, to make the Stardust Pillar susceptible to damage, you must defeat 100 (150 on Expert) minions to deactivate its shield.
Take out the Star Cells quickly so they don't overwhelm you, but be sure to also kill the little ones they split into as well. If left to long, these will grow into full-sized Star Cells again. The Milkyway Weavers are a big threat, as unlike normal worm AI, they can follow you into the air. Attack their head to kill them easily. The Stargazers should not be taken lightly either, as they have a beam attack that could easily drain a player's health.
If you are experienced, you may want to herd together a group of Star Cells and only kill the large ones, leaving the small ones alive, then wait for them to regrow. Using this tactic, you can max out the spawn limit such that nothing else can spawn, and farm out the Star Cells until the Pillar is vulnerable.
Once the final Pillar is defeated, the status message "Impending doom approaches..." will appear. About a minute later, the Moon Lord will spawn. It is recommended to have potions for the fight, as he will easily kill you if you are not prepared.
The Moon Lord, bearing a striking resemblance to Cthulhu but confirmed not to be by the developers (although at health thresholds it spawns True Eyes of Cthulhu), is summoned directly after defeating the final Celestial Pillar and serves as Terraria's final boss as of version 1.3.
There's a reason the developers chose him to be the game's "final boss". Similar to Duke Fishron, the boss sweeps side to side, taking up the entire screen and making arenas less effective than with other bosses. Recommended arenas include a minecart track or an asphalt skybridge, running along the length of the world for maximum damage output. Its defeat means subsequent runs will be easier with its drops but still provides quite a challenge even with the best gear. Luminite is used to craft end-game gear and mounts, including the Drill Containment Unit, which requires 40 Luminite Bars, or ~two Moon Lord defeats. To craft all items with Luminite, 1088 ores are required, meaning Moon Lord must be defeated 13-16 times in Normal Mode.
After defeating the moon invasions and acquiring all their drops, the player is free to do anything. You could try designing an ultimate castle or PvP with other top-tier players, or even overcome incredibly difficult challenges (e.g. Frost Moon wave 15+ with Ranger, no arena.) The only end is the player's imagination!