The Twins

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The Twins are a Hardmode mechanical boss which is essentially a more difficult version of the Eye of Cthulhu. The Twins are two separate flying entities, Retinazer and Spazmatism, connected by a tendril, each with its own attack pattern and life count. Both must be killed in order to defeat the boss.

The Twins can be summoned manually using a Mechanical Eye at night. They can also spawn naturally upon dusk with a chance of 10% once a Demon or Crimson Altar has been smashed, as long as they have not yet been defeated in the current world. If spawning this way, their arrival is announced by the status message: "". They must always be killed before dawn, otherwise, they will despawn.

While The Twins are alive, music Boss 2 will play.

Attacks

 * The eyeball with the red iris, Retinazer, fires purple lasers. It will usually attempt to remain diagonally above the player.
 * The eyeball with the lime iris, Spazmatism, fires balls of Cursed Flame. It will usually attempt to remain horizontally in line with the player.

Both alternate between their signature ranged attacks and a charging melee attack, much like the Eye of Cthulhu. Retinazer's charge attack is faster and covers a bit more distance than Spazmatism's charge attack.

Each eye has a second form which they transform to upon reaching 40% of their maximum health. Retinazer transforms at /  HP while Spazmatism transforms at  /  HP.
 * Retinazer becomes a mechanical eye with a laser turret in its pupil. It fires more rapidly and with higher damage, and periodically fires in quick barrages, but does significantly less damage. The barrages become more intense and frequent the more damage Retinazer takes, eventually occurring non-stop. In its second form, Retinazer will only shoot at the player and no longer attempt to ram into them or align diagonally with them.
 * Retinazer will, however, align horizontally with the player when firing barrages, though not as tightly as first-phase Spazmatism does.
 * Spazmatism becomes a mechanical mouth. It chases the player, charging with greater speed and range, and periodically spews streams of Cursed Flames from its mouth in a manner similar to the Flamethrower. The flames can inflict the Cursed Inferno debuff and deal high damage. In its second form, Spazmatism will no longer attempt to align horizontally with the player.

In Expert mode, Retinazer's laser firing becomes faster and charges become farther as its health depletes. Spazmatism's fireballs inflict Cursed Inferno for double the duration. Spazmatism will also charge faster in its second form.

Tips

 * In both of The Twins' second form, using items like a Cross Necklace or having Titanium armor greatly helps take less damage by becoming invincible during most of their strong "rapid attacks".
 * Try to defeat one of the Twins at a time. Having both in their second forms at near equal health will prove dangerous to any player, especially in.
 * Spazmatism should be defeated first, since its cursed flames are difficult to avoid in its second form. Retinazer is less deadly, cannot inflict debuffs and will not charge in its second form. It is also easier to outrun Retinazer and therefore get away from it quicker.
 * Because Souls of Sight are used mainly for making magic-based items, this boss is less rewarding to ranged or melee players.
 * The is an excellent weapon against The Twins if it is fired as the player runs away.
 * If The Twins are outran, such as with the case of a long railroad, it is possible to make one of them despawn. This leaves the player to fight only one eyeball; often Spazmatism due to its fast charges.

Trivia

 * Retinazer's name is a of ', a part of the eye, and '. Spazmatism's name is a portmanteau of ', an eye disorder, and ', meaning to twitch uncontrollably.
 * The Twins seem to have central.
 * In its second form, Spazmatism's eye fire functions almost identically to the Flamethrower weapon, with similar range and damage but inflicting the Cursed Inferno debuff instead of On Fire!.
 * The Twins are the only mechanical boss with phases, and the only mechanical boss that seems to be partially made of flesh, possibly being biomechanical hybrids. Unlike the other two mechanical bosses, however, they are vulnerable to more debuffs.
 * Despite inflicting it, Spazmatism is not immune to Cursed Inferno.
 * They are the only boss with two trophies.
 * Although The Twins spawn off-screen, the tendril between them can appear in the screen.
 * The Twins are one of three bosses with a minion designed after it (the Optic Staff), the others being the (the ) and Duke Fishron (the Tempest Staff).
 * The achievement appears to depict the second form of the Eye of Cthulhu rather than The Twins.
 * Both twins have a separate defeat message and the first one killed has a chance to drop the Twin Mask, doubling the chances of getting one each fight.

History
Die Zwillinge Les Jumeaux 쌍둥이 双子魔眼