Guide:The Twins strategies

The Twins are the hardmode version of the Eye of Cthulhu. They are the mid-boss of the hardmode bosses, stronger than The Destroyer but weaker than Skeletron Prime.

Terrain preparation
Space is a must when battling the Twins, as they must be dodged often.


 * A very long Sky Bridge is optimal. Continuously running with Hermes/Spectre Boots causes both of the Twins to miss you with their projectiles very often, and keeps each Twin at a stationary vertical position most of the time, allowing you to fire backward continuously at it. Wings will help dodge each of the Twins' second phases. When one Twin enters its second phase, kill it before activating the other Twin's second phase.
 * The standard Boss arena of several layers of wood 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.
 * The more maneuverability you have (Wings, Spectre Boots, and Cloud in a Balloon), the less horizontal space you'll need for your arena. Flying straight up or falling causes the majority of The Twins' attacks to miss and makes evasion much easier, allowing you to use less defensive gear. However, you must lead your shots more carefully.
 * If your arena is relatively small, hook up any heart statues and star statues you might have, with a 1 or 5 second timer. A minimum of three should be enough to keep you alive until the end of the fight. Bring mana/health potions to be safe.

Armor
Adamantite armor should be used (assuming Hallowed armor is unavailable). The defensive set bonus should generally be used, though those confident in their dodging ability may opt for the ranged bonus for extra damage.

Weapons

 * The Adamantite Repeater with Cursed Arrows is the optimal weapon for players who have yet to beat any Hardmode boss.
 * The Megashark with Crystal Bullets is optimal if The Destroyer has already been defeated. Many of the Crystal Bullets' secondary shards will hit The Twins, causing much quicker damage than any other projectile.

Other weapons that work quite well are the Clockwork Assault Rifle with Crystal Bullets, because it has reasonable damage and a good range, and the Star Cannon, if you have enough ammo saved up.

For magic users, the Laser Rifle is an effective magic weapon due to its fast firing speed, if you are lucky enough for it to drop from the Wall Of Flesh. Alternatively the Crystal Storm is an effective magic weapon that can be crafted before challenging any of the Hardmode bosses.

Accessories
Accessories that improve mobility are a must, since the Twins use quick attacks.


 * The Spectre 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.
 * The Obsidian Shield or the Cobalt Shield will prevent knockback.
 * The Philosopher's Stone is more helpful than you might think, as waiting those extra 15 seconds for the regenerative potion cooldown period is what will often kill players during this fight.
 * The Cross Necklace is another good choice, as the Twins' frequent ramming moves deal a lot of rapid damage, and the extra period of invulnerability mitigates a significant portion of this damage.

If possible, reforge all Accessories for defense bonuses (though damage bonuses will help too). If money is no object (see Guide:Making Money), having all Accessories reforged to Warding provides an extra 20 defense, which is extraordinarily helpful since unless you're very good at dodging, you will be getting hit a lot during this fight.

Potions

 * At least seven Greater Healing Potions. Ten to be safe; this will be more than enough for any Twins fight.
 * Regeneration Potion and Ironskin Potion will help prevent fatal damage. Two of each will likely cover the entire night.
 * One Bowl of Soup will likely last the entire fight.
 * Gravitation Potion can be especially useful, as it eliminates the need for any arena and may free up an accessory slot (keep in mind you will need to prevent fall damage yourself when the potion wears off, if you unequip the Wings). Three of these will last the entire fight.
 * Swiftness Potion helps you evade the twins. Two should last the entire fight.
 * If you have access to a Crystal Ball, activate it just before the fight. It will likely last the entire fight.

The battle
The Twins, as the name suggest, are two separate monsters, both of which must be killed. They have a combined health of 48,000, shared equally between them. Retinazer, distinguished by its red pupil, fires lasers. Spazmatism, distinguished by its green pupil, fires cursed flames. When reduced to half health, they will transform, gaining a slight boost in offense and defense. They will not both transform at the same time; both must be reduced to half health for both to transform. When one is destroyed, the other will continue attacking in the same pattern.

Retinazer
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 vertically with the player, positioned above them, which makes its shots easy to block with a solid ceiling.

When it changes into its second form, Retinazer will no longer engage in charge attacks. Instead, its lasers will fire with increasing frequency 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 (Preferably without fall damage), and you can be left unscratched. 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 therefore harder to dodge.

Spazmatism
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 aren't as fast and thus easier to dodge. Spazmatism is always aligned horizontally with the player.

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. However, it doesn't 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 kill first?
Though killing one or the other first is largely a matter of preference, one should always be killed before causing the other to transform. Fighting both in their second state is far more difficult.

Killing Retinazer first:

Pros: Spazmatizm has a ranged attack, and killing this Twin first will assist players who are bad at dodging, afraid of lasers, or have a relatively low movement speed.

Cons: Spazmatizm has many, many lasers to dodge, and, in addition, if you are a slow player, can be the more deadly of the two Twins to fight.

Killing Spazmatizm first: 

Pros: Melee players can get it over with, and kill the green fire vomiting one first, and then destroy the other Twin, Spazmatizm.

Cons: If, on the odd chance you are a melee player, or slow, dodging the flamethrower vomit is potentially deadly.