Guide:Defending against invasion events

This Guide covers all Events currently implemented in Terraria up until 1.3.5.3.

Blood Moon
Blood Moons are events that have a 1 in 9 chance of occuring each night once the Player has 120 life or more. During the event, the enemy spawn rate as well as the maximum amount of enemies that can be on screen increase dramatically, allowing swarms of enemies to appear at one time. Additionally, monster spawns completely ignore reduced spawn rates by way of NPCs. Zombies get the ability to break open doors during this event, posing significant danger to NPCs inside houses. New enemies such as the, , and in Hardmode, the will spawn as well.

The event is dangerous at the beginning of a playthrough, however it can also be very profitable, as the Dripplers and Blood Zombies have a chance to drop either the and, both of which being very good items. Also, the increased spawn rates will apply to every biome, making farming for important items much easier.

Generally, Blood Moons can be done safely through by simply staying in your base, as long as all doors are either prevented from opening inwards or simply barricaded by blocks.

Goblin Army
Goblins will appear at the spawn point and kill any NPCs they find. They will continually spawn until the progress bar is full, at which they are defeated. They can be spawned by using the, or with a 1/20 chance at dawn after smashing at least one /  and one player with at least 200 HP.

This group has multiple types of units with different attack patterns, so strategies for dealing with them will differ depending on the type of goblin.
 * The, a basic enemy with no special characteristics.
 * The, and shoot projectiles that go through blocks.
 * The, a fast enemy that can jump high and break open doors faster.
 * The, an enemy with very high health and knockback resistance.
 * The will shoot wooden arrows at the player.
 * Exclusive to Hardmode, the is a miniboss that can fly, shoot a stronger versions of the Goblin Sorcerer's projectile and summon . It drops an unique Shadowflame weapon when killed.

A long, flat field near the base would be the best place to deal with the army, as it would be close enough to the spawn point to appear while keeping the goblins away from the NPCs. Weapons that can do damage to multiple enemies at once such as the or  are useful for taking out crowds.

Digging a pit on both sides of your base is a simple but effective way of holding back most of the Goblins, as they won't be able to jump out if it's deep enough. However Archer Goblins will still shoot, and it won't protect the player from Goblin Sorcerers.

Old One's Army
The Old One's Army is an unique event in that it gets more advanced the further the player has progressed in the game, and the enemies won't focus on killing the player, instead they will try to destroy the used to summon it. The enemies drop an unique temporary item, the, which is used to summon Tavernkeep's Sentries and disappears when the event is over.

The event is divided in 7 (5 in the first tier, 6 in the second one) waves, each being harder than the last. When all waves are completed, the event will end and the player will be rewarded with Defender Medals and the ability to use the Tavernkeep's Sentries outside of the event. If the Eternia Crystal is destroyed by the enemies, the event will end prematurely and the player won't get any rewards.

Pirate Invasion
The Pirate Invasion can be considered the Hardmode version of the Goblin Army, with similar spawn conditions and much stronger enemies.

After smashing at least one /  it will have a ~4% chance to happen if it has yet to be defeated, subsequently having a ~2% chance to happen. It can also be summoned by the use of a.

The Pirate Invasion has multiple types of units with different attack patterns. The event currently contains six (seven on ) enemies:
 * The, who just like Goblin Peons, is an average enemy with no special attacks.
 * The, who shoots high damaging Fire Arrows with her crossbow.
 * The, a flying enemy with low health but high damage.
 * The, who shoots bullets at a very fast rate.
 * The, a very fast enemy with high knockback resistance and damage.
 * The, a miniboss with the ability to shoot high damaging bullets at a faster rate than Pirate Deadeyes. It will occasionally shoot a Cannonball that does massive damage on hit.
 * The, a flying boss enemy who will spawn other pirates and shoot Cannonballs. It can only be killed by destroying its Cannons.

Due to the high stats of all the enemies, defeating the invasion is not an easy feat at the start of the Hardmode. The Pirates should never be fought in the open, as the projectiles fired by Crossbowers and Deadeyes can easily overwhelm a player. The event can be dealt with much more easily by standing in a closed space above ground, since none of the enemies have the ability to attack through blocks.

Solar Eclipse
After a Mechanical boss has been defeated, Solar eclipses have a 1/20 (5%) chance to happen at the beginning of any day. The event will spawn very strong enemies, most of them having a special drop as well:
 * The, and  act like a Zombie, but they are much faster and possess significantly higher stats.
 * is similar, but becomes much faster when in water. It has a low chance of dropping the when killed.
 * is very fast and has the ability to crawl on walls, becoming even faster and less vulnerable to knockback when doing so.
 * deal high damage, and can turn into bats if the player is above them. They will rarely drop either the or  when killed.
 * is an uncommon enemy with the ability to shoot lasers from its eye. It drops the pet when killed.

After all three mechanical bosses have been defeated, one more enemy and a miniboss will spawn:
 * The  acts similarly to a, but with higher stats. They have a low chance of dropping when killed.
 * is the miniboss of the event. It attacks by lunging at the player, and then it will stop to lay eggs on the ground, which will hatch into Baby Mothrons if not killed. It occasionally drops the when killed and, after defeating Plantera,  and the.

After Plantera has been defeated, even more enemies will spawn:
 * The are very fast and do high contact damage. They rarely drop  when killed.
 * aren't too fast, but their high damage and defense makes them very dangerous. They can be hard to see due to their small size, so caution is always required. They drop the when killed.
 * have low health, but they throw flasks which deal heavy area damage. They have a chance to drop the when killed.
 * are slow but have extremely high health and shoot many low damaging nails. They rarely drop the when killed.
 * will spawn in an almost invisible state, and they will start attacking when the player gets close. They deal very high damage, so they must always be watched out for.

Only Mothron and Reapers have the ability to go through blocks, so fighting in a box above ground isn't as reliable if there isn't an easy exit available.

Frost Legion
The Frost Legion does not happen on its own. The player has to obtain a from a  to summon them. The summon item can only be obtained in Hardmode, but the Legion can still be summoned and defeated in a non-Hardmode world.

There are three unique enemies in the Frost Legion, named, , and.

The Snowmen are incapable of jumping down from simple wooden platforms, meaning it is possible to construct a basic trench with a wooden platform above it, and be completely out of harms way.

If you place lava pits on either side of your house, you can defeat most of the snowmen that spawn, however, Snow Ballas may obstruct the traps by throwing blocks, making them less effective. Filling the empty space of any traps with Platforms will prevent Snow Ballas from blocking up the traps. They occupy the same layer as other furniture and do not block movement.

Frost Moon
The Frost Moon is a Hardmode Post-Plantera event, in which Christmas-themed enemies invade the world. It can only be started by crafting and using a during night. The event consists of 19 waves, with a Final Wave 20 after all of them have been completed.

Pumpkin Moon
The Pumpkin Moon is a Hardmode Post-Plantera event, in which Halloween-themed enemies invade the world. It can only be started by crafting and using a during night.

The event consists of 14 waves, and then a Final Wave 15 which will last until the night is over.

Martian Madness
The Martian Madness is a post-Golem event. It will only happen when the Player finds a in the wild, and then lets it escape into Space.

During the invasion, the player will find many strong enemies with different attacks, such as:
 * , which are the basic enemy of the event.
 * , who possess a similar behavior, but with lower stats and the ability to shoot lasers from their gun.
 * Occasionally, it will spawn riding on a, becoming a Scutlix Gunner. The Scutilx moves very fast, deals high contact damage and its rider will shoot lasers, making this a deadly enemy. The Scutlix Gunner has a low chance to drop the , which will allow the player to ride a Scutlix of their own.
 * are a very fast enemy that can quickly shoot lasers, have a lot of health and are immune to knockback. Due to their tall size and low jumps, they can easily get stuck on blocks.
 * are small enemies with low damage and health. They can only attack by charging at a player, self-destructing itself on contact. It's the only enemy in the invasion that can go through blocks.
 * behave like Gray Grunts, but they inflict the debuff on hit, which causes a player to rapidly lose health when moving.
 * have low stats but instead of attacking, they can deploy, which shoot an electric projectile at the player, which inflicts the Electrified debuff. The Engineers should be killed quickly, as they can easily overwhelm a player with Turrets.
 * spawn protected by a Bubble Shield, which will need to be killed before the player can harm it. If the Officer isn't killed quickly after the Bubble Shield is destroyed, it will activate again.
 * are similar to Ray Gunners, with their projectile inflicting the debuff on hit.
 * The is the boss of the event. It will alternate between firing lasers from its turrets at the player's position, shooting homing missiles from its Cannons, and then following the player while attacking with its Deathray. After its Turrets and Cannons have been destroyed, the player will be able to damage its Core, and its Deathray will deal much more damage. The Saucer will also move more aggressively than before. When killed, it will drop an unique weapon or item.

Like other events, almost all enemies lack the ability to directly attack or go through blocks, so standing in a closed space can be a good idea, especially since the Martian Saucer is very hard to defeat in the open.

A Lava pit is also efficient, since it will deal with the grounded enemies while the player focuses on the Martian Saucer. Note that Lava will kill the Scutlix before the Scutlix gunner, so this shouldn't be done if the player wants the Brain Scrambler item.

An example of a lava pit, complete with heart/star statues and traps hooked up to a timer.

Lunar Events
The Lunar event will happen when the Lunatic Cultist boss is defeated. The invasion consists of four Celestial Pillars on a specific place in the world. Each of them focus on one of the Four main classes: Melee, Ranged, Magic and Summoner are represented by Solar, Vortex, Nebula and Stardust Pillar respectively.

When near a Pillar, many different enemies will start attacking the player. In order to damage the Pillar, the player will need to kill 100/ of the enemies to destroy the Shield protecting it.

After all four Pillars have been defeated, the message "Impending Doom Approaches" will appear, and the Moon Lord will spawn shortly after.

Cannons
The and the, purchased from the Pirate, bring a lot of firepower to protect a base. Keep in mind that you have to be next to the cannon (and have ammunition for it) to use it effectively; when used remotely with wires the cannon's projectiles do not inflict any damage.

Lava
Lava is a useful tool for easily killing enemies. By placing a single bucket of lava in a sufficiently wide 1-block-deep trench, it is possible to create a pool shallow enough to kill off most enemies while preserving their loot (such traps can be tested easily by throwing cheap items into the trench—if they burn up, the pit needs to be wider).

Note that enemies killed by Lava will not be counted by the and will not contribute to banners.

Lava Moat
Since monsters cannot spawn on lava, you can force monsters to spawn in a reduced area to more effectively affect them with traps, sentries, and other attacks. Create a "spawn surface" ten-to-fifteen blocks wide. Surround it by lava moats about 40 blocks wide on both sides, and fill up any nearby holes or cave. While the event is happening, make sure to keep the spawn surface out of sight, for instance by standing on a platform high enough above it.

This will make the enemies spawn in one, concentrated area where they can easily be killed by Traps, lava or Area of Effect weapons.

Sentries
Events are the ideal situation for using sentry summons, as they are powerful but stationary defenses, and you have to defend an area. Using an armor set from the Tavernkeep to allow to summon several sentries will let you take care of most regular enemies as quickly as they arrive, allowing you to concentrate on the stronger menaces. With a Bewitching Table and a you can combine sentries with a few more mobile minions for assistance. Sentries can also be combined with weapons that have a lasting area of effect, such as the and the.

Traps
Traps can be used to help damage enemies. Dart Traps can be found throughout the Underground and especially in the Dungeon, Geysers are found in the Underground, and Super Dart Traps, Flame Traps, Spear Traps, and Spiky Ball Traps are all found in the Lihzard Temple.

When multiple traps are used, they should be staggered so as not to all hit at the same time: an enemy hit by a trap will be briefly invulnerable due to its piercing properties, so if a monster is hit by two simultaneous darts, only one will damage it.

Dart Traps and Super Dart Traps can protect the sides of your base from low-level threats, such as the Blood Moon zombies, especially if rigged to automatic activation mechanisms such as Timers, or Pressure Plates in an engine. Flame Traps, Geysers, Spear Traps, and Spiky Ball Traps are more powerful but are best used with methods to keep enemies clustered in a small area, such as a death pit, a hole deep enough that they cannot jump out.

Traps can be placed in the background by using, actuating them once, then removing the actuators so that further activations will not place them back in the foreground. This is useful for staggering traps, as a background traps will not block the path of another Trap's dart, spear, spiky balls, or flames.

Note that enemies killed by Traps will not be counted by the Tally Counter and will not contribute to banners.

Tower of Death
If you are in Hardmode and have acquired the Nimbus Rod and Wings or anything that allows flight, there's a very efficient and safe way to farm or survive most of these events by making a tall tower, 20 blocks or higher, at least 4 blocks wide, with two entrances from the ground for enemies to come in. At the top of the tower, place some Platforms right under you, enough to cover the width of it.

When an event occurs, place the two Nimbus Rod's Clouds on the platforms, and you will have a safe method to kill grounded enemies. Flying enemies will fly around the tower, so a weapon that can attack through blocks is recommended.

In Solar Eclipses however, the Mothron miniboss can go through blocks, making the strategy ineffective.

Invincibility Machine
This technique involves overriding all forms of damage with the temporary invincibility granted when damage is taken from a weak enemy such as a statue-spawned slime. This is useful when dealing with Moon events, such as the Pumpkin Moon and Frost Moon, though it also works against bosses (with the exception of the Moon Lord, for whom special measures were put in place to prevent this). The machine fails if the protective slime is killed.

The machine consists of a small 5x6 box half-filled with Honey, such that the player will receive the Honey Regeneration buff, but without drowning. A Teleporter provides an easy way into the machine, and various switches are available to toggle traps and the actuated spawn surface. The Teleporter is optional; you could just actuate yourself in from the top.

It's important to note that the machine will only work if the protective slime is the oldest enemy on-screen. This way, the slimes spawned from the statue will have damage priority over any other mobs that spawn thereafter. Lastly, reactivate the spawn surface before starting the event. If any NPC is killed while the machine is in use, then it will fail.

The downside of an invincibility machine is that the player's options become limited. Generally, the best approach is to use a summoner build with the highest-damage summoning armor available and five damage-increasing accessories (Summoner Emblem, Papyrus Scarab, Necromantic Scroll, Hercules Beetle, and Avenger Emblem - all with the Menacing Modifier). Most summoning weapons can attack enemies outside while preserving the protective slime. The exceptions are the Tempest Staff, Stardust Dragon Staff, and Rainbow Crystal Staff. The Stardust Guardian will kill the slime if placed too close to the player, but it is okay to summon it at a distance.

One of the few weapons that can be used from within the box is the Blizzard Staff, as its projectiles cannot enter the invincibility machine. The Meteor Staff can be used the same way, but the box must be constructed with a thicker ceiling, because the explosions can potentially kill the slime. Spears cannot be used, as the slime will periodically jump near the player's head area and enter the damage hitbox of the spear. In the late game, one can also set up a Staff of the Frost Hydra and Lunar Portal Staff for free damage. The Lunar Flare may be used to eliminate faraway enemies to either side, but any explosion that occurs too close to the machine will kill the slime. It also might not be a bad idea (if the player does not have the Cobalt Shield or any of its upgrades) to grapple to the side of the machine, because being knocked around by a slime is a little bit annoying (though it won't compromise the integrity of the machine). You can also simply place two target dummies next to each other, then build a row of any kind of block (with the the exception of falling blocks and platforms) 8 tiles above the ground you put the target dummies on. Next step: get yourself a slimy saddle, and hop on the target dummies. Be careful not to hit the dummies with any weapons. Besides, you won't need weapons anyways. The slime will damage anything that hovers close to your player.

A better option may be is to place 2 target dummies close to each other then placing any blocks 4 blocks above the dummies. Now ride the slimy saddle and you will be invincible to most attacks. When a player bounces onto an enemy while riding a slimy saddle, both player and the enemy will gain an invincibility frame. Since the enemy gains a longer invincibility frame, by setting up two target dummies, you will always be invincible. Just do not use any piercing damage or else you will fall and you will take damage. Note that this tactic does not work for the Moon Lord and the dungeon guardian.

Another idea would be to set up a teleporter circuit that constantly teleports you between rooms with heart statues lined up on the walls in each. This could also be combined with the idea above. With this setup, the player could teleport around, avoiding attacks and healing while under the immunity of the slime's attacks. However, this would make the project harder to set up as the player would have to build multiple copies of each room.