Main article: Bosses
The Twins are the Hardmode version of the Eye of Cthulhu. They spawn as two eyes, one with 20,000 HP (Retinazer) and one with 23,000 HP (Spazmatism). Unlike the Eye of Cthulhu, they do not immediately transform at half health – Retinazer transforms at 8,000 HP and Spazmatism transforms at 9,000 HP. These values are increased in Expert Mode. The Twins are summoned by using a Mechanical Eye at night. It is worth noting that The Twins will gain defense in their second forms, unlike the Eye of Cthulhu.
The two eyes have different fighting styles. Spazmatism focuses on slamming into the player and firing cursed flames. Once it reaches its second form, it will resemble a mechanical version of the Eye of Cthulhu’s second form. It will deal a lot more damage, and the flames it shoots are more consistent like the Flamethrower instead of the Cursed Flames, but the flames will still inflict Cursed Inferno debuff on the player.
The other eye, Retinazer, focuses on shooting the player with Death Lasers like the Destroyer’s Probes. Once it reaches its second form, it will replace its pupil with a laser cannon. During this form, it will shoot lasers extremely fast, sometimes having the same fire rate as a Megashark. The last Twin destroyed will drop all of the loot.
In Expert Mode Retinazer’s HP is 30,000, while Spazmatism’s HP is 34,500. Spazmatism’s charging attack will also be similar to the Eye of Cthulhu’s chain dash ability in its second form, and Retinazer will shoot lasers almost as rapid as the Wall of Flesh at 500 HP.