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 (7:30PM to 4:30AM). They also have a chance to spawn naturally at dusk once a Demon or Crimson Altar has been destroyed, as long as they have not yet been defeated at least once in the current world. If spawning this way, their arrival is announced by the status message "".

The Twins must be killed before dawn, otherwise they flee and despawn.

Eyes
There are two eyes: Retinazer and Spazmatism. Retinazer is a laser-shooting eye with a red iris; Spazmatism is a similar-textured eye, though it has a green iris. It fires green Cursed Flames.

First phase

 * The eyeball with the red iris, Retinazer, fires purple, high-velocity Eye Lasers. It will usually attempt to remain diagonally above the player.
 * The eyeball with the green iris, Spazmatism, fires medium velocity balls of Cursed Flame. It will usually attempt to remain horizontally in line with the player.

Both alternate between their signature ranged attacks and charging melee attack, much like the Eye of Cthulhu. Retinazer's charge attack has higher velocity but has longer periods between charges and does less charges than Spazmatism's.

Second phase
Each eye has a second form, which each individually reaches upon its health dipping to 40%. Retinazer transforms at 0 / /  HP while Spazmatism transforms at 0 /  /  HP.
 * Retinazer becomes a mechanical eye with a laser cannon in its pupil, and only fires red Death Laser projectiles, ceasing its attempts to ram the player (or align with the player diagonally). It fires more rapidly and with higher damage, and periodically fires in quick barrages which does significantly less damage. The barrages become more intense and frequent the more damage Retinazer takes, eventually occurring non-stop.
 * Retinazer will, however, align horizontally with the player when firing barrages, though not as tightly as first-phase Spazmatism does. When not barraging, Retinazer will usually align vertically with the player.
 * Spazmatism becomes a mechanical mouth (similar to the Eye of Cthulhu) that chases the player, charging with greater speed and range, and periodically spews Eye Fire from its mouth, streams of Cursed Flames, in a manner similar to the Flamethrower. The flames can inflict the Cursed Inferno debuff and deal high damage. It no longer attempts to align horizontally with the player.

In, Retinazer's laser firing becomes faster and charges cover more distance as its health depletes. Spazmatism's fireballs inflict Cursed Inferno for /  the duration. Spazmatism also charges faster in its second form.

Tips

 * Focus on defeating one eye completely first without inflicting too much damage on the other one. Battling The Twins while both are in their second form makes the battle much more difficult, especially in.
 * Spazmatism may be a better choice for defeating first, since its Cursed Flames are difficult to avoid without proper mobility equipment and buffs in its second phase. Retinazer is less deadly, as it cannot inflict debuffs and will not charge in its second phase, which helps the player get some distance if they are a ranger.
 * The Twins are only immune to Confused and Poisoned, so using a weapon that inflicts a debuff may be useful during the fight.
 * A good arena for this boss is simply a long, flat plane. With Lightning Boots (or better) and a ranged or magic weapon, the player can continually outrun The Twins' attacks while firing back at them.
 * In its second phase, Retinazer can only attack the player if it has an unobstructed line of sight. Hiding in a box prevents it from dealing any damage.
 * A Gravitation Potion can be an excellent method of keeping distance from the Twins, allowing them to be attacked freely.

Trivia

 * Retinazer's name is a of ', a part of the eye, and '. Spazmatism's name is a portmanteau of ', meaning to twitch uncontrollably, and ', an eye disorder.
 * Spazmatism's second form has visible bolts along either side, whereas Retinazer's second form only has them along one side.
 * The Twins seem to have complete (two different eye colors).
 * In its second phase, Spazmatism's Eye Fire attack 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 boss with two trophies, and the only with more than one phase.
 * Despite inflicting it, Spazmatism is not immune to Cursed Inferno.
 * The Twins are one of three bosses with a corresponding minion (Optic Staff), the others being the  and Duke Fishron (Tempest Staff).
 * The Twins are usually considered the hardest of the mechanical bosses, but it is arguable.
 * The Twins seem to be bio-mechanical hybrids since they are not immune to debuffs like On Fire!, Poisoned, or Acid Venom, even when transformed.
 * The Twins seem to be bio-mechanical hybrids since they are not immune to debuffs like On Fire!, Poisoned, or Acid Venom, even when transformed.