The Twins

"This is going to be a terrible night..."

The Twins (one of the three Mechanical Bosses) are the Hardmode version of the Eye of Cthulhu. The Twins are two separate flying entities 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 are summoned using the Mechanical Eye at night, and must be defeated before dawn, otherwise they despawn. They also have a chance of spawning on a random night once Hardmode begins, if they have not been defeated yet. Their approach is signaled at dusk via the chat message, "This is going to be a terrible night..."

Attacks

 * Retinazer has an orange-red iris and fires purple lasers. It will usually attempt to remain vertically above the player.
 * Spazmatism has a green iris and fires balls of Cursed Flame. It will usually attempt to remain horizontally inline with the player.

Both alternate between their signature attacks and a charging melee attack, much like 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 phase. Retinazer transforms at 8000HP, while Spazmatism transforms at 9000HP.
 * 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. The barrages become more intense the more damage Retinazer takes. In its second form, Retinazer will only shoot at the player(s) and no longer attempt to ram into them.
 * 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 Expert mode, Retinazer's laser firing become faster and charges become farther as his health goes down.
 * in Expert Mode Spazmatism will fire Ichor flames and will fire them slighty faster.

Achievements
Buckets of Bolts is the achievement you earn for defeating The Twins, The Destroyer, and Skeletron Prime for the first time.

Mecha Mayhem is the achievement you earn for defeating the three Mechanical Bosses in one battle together.

Tips

 * In its first form, Spazmatism's flame shots often miss, even if the player isn't moving. The same goes for Retinazer's lasers in its second form.
 * Concentrate on killing Spazmatism completely first. Fighting them both in their second phases simultaneously makes the fight significantly more difficult.
 * Both of the Twins are vulnerable to the Frostburn and Ichor debuffs.
 * 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"
 * If the Twins are ever out-run, such as with the case of a long railroad, they will despawn regardless of the time of night.

Trivia

 * Retinazer's name is a portmanteau of retina, a part of the eye, and laser. Spazmatism's name is a portmanteau of astigmatism, an eye disorder, and spasm, meaning to twitch uncontrollably.
 * The Twins are the only Hardmode Mechanical Boss with phases, and is also the only mechanical boss that seems to be partially made of flesh, possibly being biomechanical hybrid.

History

 * Spazmatism now transforms at 9000HP and Retinazer now transforms at 8000HP, instead of at half HP.
 * Now only drops 15-30 Hallowed Bars.
 * One of the twins can no longer despawn as long as the other is still active.

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