- 1 Spawn Condition
- 2 The Fight
- 3 General Strategies
- 4 Specific Strategies
The Twins can be spawned by fulfilling any of these conditions:
- Smash a Demon / Crimson Altar. They will then have a 10% chance of appearing when night falls. Note that this condition is shared with the rest of the trio, which increases as more mechanical bosses are defeated, and thus it's not guaranteed if they have yet to be defeated, and will only work if The Twins have yet to be defeated;
- Use a Mechanical Eye during Hardmode at night.
It must then be defeated before the night ends.
The Twins, as the name suggests, are two separate monsters, both of which must be defeated. They have a combined health of 43,000 / 64,500, shared between them. Retinazer, distinguished by its red iris and that it fires lasers. Spazmatism, distinguished by its green iris and that it fires cursed flames.
When reduced to 2/5 health, they will transform, gaining a slight boost in offense and defense. Each Eye transforms independently once reduced to 8,000 / 12,000 HP (Retinazer) / 9,200 / 13,800 HP (Spazmatism); the other eye remains in its original form until it is reduced to the appropriate amount. When one is destroyed, the other will continue attacking in the same pattern.
It is a good idea to take them out one at a time, because if one dies first, it will be much easier to defeat the other one.
In its first form, Retinazer will fire lasers at the player at a steady but somewhat slow rate. This is occasionally interrupted by charging attacks, which mirror that of its partner. Retinazer does slightly less damage than Spazmatism, but this is offset by its higher accuracy thanks to the speed of the lasers. When not charging, Retinazer will always be aligned diagonally with the player, positioned above them.
When it changes into its second form, it will no longer engage in charge attacks. Instead, its lasers will progressively fire at a faster rate as it loses health. This is occasionally supplemented by a weaker but much more rapid laser attack that tracks extremely well. To avoid this, try to fall as fast as you can, and you can be left unscathed. With wings it is possible to "zig-zag" up and down to dodge the lasers. This is made trickier as the fight goes on, with Retinazer using more rapid and fast lasers that are much harder to dodge.
Spazmatism, like Retinazer, varies between firing Cursed Flames from a distance and engaging in charging attacks. The flames do more damage than the lasers, but are not as fast and thus easier to dodge. However, the Cursed Inferno debuff can be very dangerous for its high damage over time and its ability to stop health regeneration. Its charge attacks are faster and more agressive than Retinazer.
Spazmatism's second form changes his attack pattern dramatically compared to Retinazer. Its cursed flame attack becomes a constant stream of flame, which will last for several seconds (and deal large amounts of damage). However, it does not chase the player quite as quickly as it does in its first form, making avoiding the attack somewhat easier. Once it stops spewing flame, it will charge with greatly increased speed, which also does a lot more damage. Dodging these charges is quite difficult. Much like Retinazer, fall as fast as you can while he is charging, and you should be okay. Misdirecting Spazmatism's charges is easier than it sounds; if you jump as he slows down, he will charge over you. This causes Spazmatism to charge at you from either above or below, making him easier to dodge if you just run.
Which to defeat first
The following lists shows Pros and Cons by defeating one of the Twins. Players generally kill Spazmatism first.
Defeating Retinazer first:
Pros: Retinazer has a ranged attack, and defeating this Twin first will assist players who are bad at dodging, afraid of lasers, or have a relatively low movement speed.
Cons: Retinazer has many, many lasers to dodge, and, in addition, if you are a slow player, defeating Retinazer can be the more difficult of the two Twins to fight.
Defeating Spazmatism first:
Pros: Damage from Cursed Inferno can easily add up, so if you defeat him first, you won't have to deal with that for as long. Keeping Retinazer in its first form can allow you to easily heal to full before killing it.
Cons: Attempting to defeat it as either a slow or melee player (unless you have a melee weapon that shoots a projectile like the Beam Sword or the Ice Sickle) can make dodging the eye fire more difficult.
This content is transcluded from Guide:Practical tips § Combat.
- Starting the battle just after the sun sets (7:30 PM) will provide the maximum amount of time to defeat nocturnal bosses. In Hardmode, the Moon Charm and/or Moon Stone and their upgrades are also useful at night.
- Prepare your Boss-fighting arena with adequate lighting, Campfires and Heart Lanterns for health regeneration, and Stars in Bottles for mana regeneration if you use magic. Bast Statues will provide a significant defensive boost. Garden Gnomes and (if underground) proper torch placement will reduce damage taken and increase damage dealt due to the luck. Note Torch God's Favor helps with this. Honey pools can also be used for extra health regeneration.
- Sunflowers provide the Happy! buff to players within a 50-tile radius, which grants a +10% movement speed bonus and 17% reduction in enemy spawn rate.
- Always carry around one stack of the highest-tier healing potion available (Lesser, Normal, Greater, or Super Healing Potions). Relying only on natural Health Regeneration is not a good idea.
- It is suggested to build houses for the Dryad and the Nurse NPCs in your arena. The former casts the Dryad's Blessing buff, which increases your defense and provides you with a thorns-like effect, while the latter can heal and remove debuffs instantly, at the cost of some coins.
- Bosses are displayed on the Minimap: Follow the boss's icon to track it when you're struggling to find it. You can identify the boss icons by checking their respective wiki pages.
- Once you have freed the Mechanic in the Dungeon, you can use Wire to enhance your arena with Traps and helpful Heart and Star Statues. The former helps to damage the enemies, though be careful to set them up correctly in order not to hurt yourself during the battle. The latter will spawn heart and star pickups, respectively. Connect these devices to timers.
- It may be useful to summon and kill the Eye of Cthulhu or King Slime before summoning any harder boss in order to spawn an extra one-use pool of Hearts. Note that this will prevent any Heart Statues from spawning new Hearts.
- Remember to use the Sharpening Station, Ammo Box, Crystal Ball, Bewitching Table, and Slice of Cake before you go to explore or battle bosses/invasions. These will give boosts that are useful to take, with the first four being class-specific. They give Sharpened, Ammo Box, Clairvoyance, Bewitched, and Sugar Rush, respectively.
The Sky above the surface is highly recommended for the Twins arena, as vertical movement is required to dodge most of the attacks.
- A very long Sky Bridge (if possible made out of Asphalt or Frozen Slime Blocks) is optimal. Continuously running with Spectre / Lightning / Frostspark / Terraspark Boots causes both to miss you with their projectiles very often, and keeps each Twin at a stationary horizontal position most of the time, allowing you to fire continuously at it without switching your aim. Wings will help dodge each of the Twins' second phases. Using Asphalt can negate the need for Boots, while using them can allow you to avoid taking damage completely. However, try not to run too fast if you use Boots and Asphalt, as Retinazer may fall behind and despawn. Spazmatism, however, is fast enough to keep up. Regular stone blocks can be used too if you have obtained the Blessed Apple.
- The standard Boss arena of several layers of Platforms may be of use, as it allows firing and maneuvering in any direction. A solid ceiling just above your top platform will block Retinazer's beam attacks, as Retinazer always flanks from above.
- Also, a wall on both sides of a small area can block Spazmatism's cursed fire, but be careful not to run out of time from covering behind the wall. It is helpful to have a one block hole one block up to shoot through. This is more useful if you want to try tanking the boss with the above tip of heart statues. If you can tank the hits with the help of heart statues, you can gun down Retinazer while Spazmatism is only able to charge at you.
- A safety box in the ground isn't bad either, if you acquired the Daedalus Stormbow. That way you could attack Retinazer while its laser can't hurt you in the box. In order to attack Spazmatism make the box one block from the surface and bring Holy Arrows, the impact from the stars could hurt it. Stay close to the edge so the Cursed flames can't hurt you.
- You can also use Minecart Track when building a sky arena to avoid the Twins attack while doing a ton of damage with ranged weapons.
If you already defeated at least one of the Mechanical Bosses, you can explore the Underground Jungle for 20 Life Fruits. These will increase your maximum life to 500, which can help to defeat the rest of the Mechanical Bosses.
- Adamantite armor provides the greatest overall increase to all stats. Melee and ranged users should substitute in a Frost Breastplate to increase damage output and defense without sacrificing anything important.
- Titanium armor is a great choice due to its also high stats and the Titanium Barrier / Shadow Dodge buff.
- Crystal Assassin armor has respectable defense and stat boosts, which makes this set a viable alternative to Hardmode ore sets. On Desktop version, it provides a dash as part of its set bonus, allowing players to replace Shield of Cthulhu with another accesory.
- Orichalcum armor provides very high critical strike chance and its set bonus can hit both eyes.
- Palladium armor provides lower stat bonuses, but the Rapid Healing buff greatly increases natural regeneration.
- Hallowed armor becomes a great choice if you have already defeated a Mechanical Boss. In the Desktop version it gives you the Holy Protectionset bonus, which allows to dodge some attacks.
- Spider armor is the best choice for summoners.
- Obsidian Armor provides strong bonuses to whips, making it a strong alternative for summoners. The increased range and speed greatly increase the Firecracker's effectiveness, potentially outperforming the Spider Armor.
- The armor sets available from the Tavernkeep combine summoning with one of the other classes. This is only available if you've defeated another mechanical boss.
- Forbidden armorand Frost armor( ) provide weak stat bonuses, but allow you to mix different damage types. On Desktop version, the Frost armor provides excellent stat increases as a set bonus, making it a strong alternative to Adamantite or Titanium armors.
- For Melee users
- The Shadowflame Knife shoots very fast and deals a lot of damage per dagger. It also inflicts Shadowflame, which deals 15 damage per second, more than any other debuff available. If aimed right, it can manage to hit both eyes at the same time.
- Ice Sickle could also be used, as Spazmatism will spend most of the time behind you, so shooting constantly backwards with the piercing projectile will hit him multiple times and deal quite reasonable damage.
- Alternatively, Light Discs can work too, if you already defeated The Destroyer or Skeletron Prime.
- Yoyos with the Yoyo Bag can be useful.
- Dao of Pow and Drippler Crippler can be an excellent choice due to their high damage and range. However, they can be harder to acquire than other options available.
- For Ranged users
- The Adamantite or Titanium Repeater with Holy Arrows or Ichor Arrows is the optimal weapon for players who have yet to beat any Hardmode boss.
- Guns such as the Megashark, Uzi, Gatligator, and Clockwork Assault Rifle can be quite effective when paired with Ichor, Crystal Bullets Or Cursed bullets.
- Keeping an Endless Musket Pouch on hand is a good idea just in case you run out of ammo.
- Daedalus Stormbow is a great bow, especially if combined with Holy Arrows, even better with a Magic Quiver, as these three together can take down any of The Twins in seconds.
- The Sharanga with Wooden Arrows will be very useful as well, as it turns into Spectral Arrow .
- The Dart Rifle /Dart Pistol with Crystal Darts or Ichor Darts is an effective weapon, especially the former, which can hit both Twins at the same time.
- The Onyx Blaster with Exploding Bullet is a great combination, and will deal over 250 damage per hit.
- For Magic users
- Sky Fracture is one of the strongest weapons mages can use in early Hardmode.
- The Meteor Staff and the Crystal Serpent are also very powerful choices.
- The Spirit Flame is a highly damaging weapon that is also consistent thanks to its homing properties.
- The Shadowflame Hex Doll can also be very strong, despite its short range.
- If you have Crimson, a good idea is to get the Golden Shower, which is highly effective as it increases the damage greatly thanks to the Ichor debuff, even when not used.
- It's nice to have a Nimbus Rod, since the clouds can deal a good amount of damage if used properly.
- If a Mechanical Boss has already been defeated, the Unholy Trident is a powerful choice with confident aim.
- For Summoners
- The Spider Staff is the best summoning choice because the spiders will latch on while they change forms, dealing hundreds of damage. Note that your arena will need to include background walls to make full use of the spiders.
- The Sanguine Staff is the best summoning choice for those who don't want to make a background wall arena, due to the bat's flying ability and high damage.
- The Blade Staff's fast attacks and reliable targeting makes it a viable choice. They're at their fullest potential when boosted by Whips' Tag Damage.
- The Firecracker can greatly increase the damage output of your summons, especially the Sanguine Staff. The Durendal is a excellent choice if you already have defeated a Mechanical Boss.
- The Queen Spider Staff also is worth running, as it doesn't count towards your total minions summoned.
- If a Mechanical Boss has already been defeated, the Ballista Cane is a powerful choice when facing the Twins.
Accessories that improve mobility are a must, since the Twins use quick attacks.
- The Amphibian Boots, Frostspark Boots, or Terraspark Boots and Wings are a must, especially for the Sky Bridge method. They allow the player to dodge, and also allow the player to flee temporarily if health is running low.
- Even though it doesn't prevent Cursed Inferno, the Ankh Shield can still be used to prevent Knockback and for some useful extra defense.
- An Emblem of your respective class is a must have in Hardmode because of its big damage buffs.
- If playing in Expert mode, the Shield of Cthulhu is an incredibly useful item as well, with its dash being great for dodging.
- The Expert-exclusive Worm Scarf can greatly reduce damage taken.
- The Brain of Confusion is very useful for Expert Mode players with Crimson, as it provides a chance to dodge an attack . It doesn't prevent getting inflicted with the Cursed Inferno debuff, however.
- The Charm of Myths provides a helpful boost to newer or slower players taking too much damage by reducing the cooldown of Potion Sickness as well as increasing passive health regeneration, it can also be used by quickswapping it from the vanity slot, since the effect only applies when consuming a Health Potion.
- The Cross Necklace or the Star Veil are good choices, as the frequent charging attacks deal a lot of rapid damage, and the extra period of invulnerability mitigates a significant portion of this damage.
- The Moon Charm is very helpful if you use Melee, as it will give a minor boost to all stats, raising your defense and therefore survivability, as well as giving higher damage.
- The Magic Cuffs (or Celestial Cuffs) are helpful if you're using Mana consuming items as you will take damage frequently from The Twins.
If possible, reforge all Accessories for damage, crit chance or defense bonuses. If money is no object (see Guide:Making Money), having all Accessories reforged to Warding, Lucky or Menacing provides an extra 20 defense, 20% crit chance or 20% damage (24%, since the Demon Heart allows you to have 6 accessories, up to 28% in Master Mode with 7 accessory slots).
- Regeneration Potion, Endurance Potion and Ironskin Potion will help prevent fatal damage. Two of each will likely cover the entire night.
- Any food item providing the Well Fed buff is very useful.
- Gravitation Potion can be especially useful, as it eliminates the need for any arena and may free up an accessory slot.
- Swiftness Potion helps you evade the twins. Two should last the entire fight.
- Featherfall Potion can greatly increase mobility in midair.
- If you have access to a world with Corruption, a Wrath Potion is a good bonus, but not necessary.
- For magic users, a Magic Power Potion and a Mana Regeneration Potion are almost mandatory.
- Archery Potion will greatly boost the damage and speed of Arrows.
- Melee users greatly benefit from the effects of an Ale or Sake
- Summoning Potion is absolutely vital for Summoners attempting this fight.
- Because the Twins are vulnerable to many debuffs, melee players as well as summoners can take great advantage of Flasks. The Flask of Ichor greatly increases the damage output of all weapons, and the Flask of Cursed Flames(or Fire if you're in a Crimson world) can give a very slight increase to DPS. Similarly, Spider minions can keep them afflicted with Venom, rangers can use Frostburn or other special arrows, and mages can use a Poison Staff or other weapons that inflict debuffs, such as the Shadowflame Hex Doll.
- The Ice Rod is useful against Retinazer because the spawned ice blocks can block his lasers.
- Always stick with a weapon, never use variety unless you are forced to.
This strategy requires you take out Spazmatism first, once you defeat Spazmatism you need to get Retinazer into its second form. Then go inside a small box of solid blocks and use Summons (preferably with summon armor too), the Meteor Staff or the Daedalus Stormbow (preferrably with Holy Arrows and the Magic Quiver/its upgrades) to take down Retinazer. Because Retinazer does not charge in its second form and its lasers do not pierce blocks you will be completely safe.
Close-ranged Unicorn Strategy
A strategy that is helpful for players is a Skybridge using a Blessed Apple and any kind of yoyo (A Yoyo Bag is recommended) or a long range weapon. Running with the Unicorn and shooting the yoyo behind you will deal a lot of damage and you won't get hit very much as the unicorn is slightly faster. Warning: Using this strategy may lead to the The Twins despawning if you go too fast.
A strategy that is helpful for all classes is to use a minecart track extending as far as possible. For shorter minecart tracks, both ends can be hammered to allow the minecart to go in both directions without losing speed. As the minecart can go faster than The Twins, the player can use a long range weapon, such as a Repeater or a Yoyo (with Yoyo Bag) to deal damage from a relatively safe distance. Warning: Using this strategy may cause The Twins to despawn if that player travels too fast.
After gaining access to the Tier 2 equipment sold by the Tavernkeep, the fight becomes much easier to do. Wearing the Squire armor and using the Ballista Cane will give the best results because of the high defense and health regeneration provided by the armor, as well as the Ballista Panic! buff doubling the firing rate. Acquiring one of the accessories dropped by the Ogre is recommended for this method. When building your arena, be sure to use platforms whenever possible to maximize the opportunities your Ballistas have to fire. Make sure that you have Heart Lanterns and Campfires set up to give yourself the most health regeneration. Having a good pair of Wings, the Cobalt Shield or its upgrades, and the Lightning Boots, Frostspark Boots and Terraspark Boots are recommended for maximum mobility. The Summoner Emblem will make the fight go much faster, rounding out your accessories. A few Greater Healing Potion are all the healing you'll need in case you get backed into a tight spot. Once the Twins have been summoned in, simply kite them around your Ballistas, taking damage periodically, preferably from Retinazer's laser for minimal damage. With the best Modifiers on your gear and all the relevant buffs, the Twins will go down in two to three minutes. If you find yourself taking too much damage and needing to heal more, consider swapping out the Summoner Emblem with a Charm of Myths so you can heal more often.
Invincibility Machine 
Warning: Many players will consider invincibility machines as cheating.
After beating up the Biome Mimics, you should have Fetid Baghnakhs and Daedalus Stormbow. With two Target Dummies and a block overhead you can make the invincibility machine. Get a Slimy Saddle and try to bounce on both dummies while keeping it rapid. After you summon the boss, use the Fetid Baghnakhs to quickly take out Spazmatism. Then use the Daedalus Stormbow to beat Retinazer.
Note: In the 1.4 update, this glitch was changed to be much harder to pull off, making it nearly impossible. Try this at your own risk, as it might not work.
The Black Spot
It is very easy to defeat The Twins with The Black Spot. The only thing you need is stable and high enough damage to beat them until dawn. Keep in mind that circling around in the skies may summon a Wyvern, so it's nice to have a weapon against segmented enemies, such as the Medusa Head.
Note: The Black Spot was nerfed to be slightly slower, this may result in taking more damage than intended.
Bouncing Strategy 
It is very effective if you are able to keep The Twins low to the ground to bounce on them repeatedly using a Slimy Saddle. It works especially well to pair this with the Meteor Staff, raining meteors down on whichever eye you happen to be bouncing on.