It is spawned at the beginning of the night while an active Terrarium exists in the world, targeting a player and spawning near them regardless of the location of the Terrarium. If a player fails to kill the Eye of Terror during the night that it is spawned, it can be summoned again the next night with the same amount of HP remaining if the Terrarium is activated again. For each full night spent without reactivating the Terrarium, the Eye of Terror heals itself for 250 HP.
Upon spawning, the Eye of Terror charges towards the player, dealing area of effect damage, then spawns one Egg of Terror which will hatch into a Suspicious Peeper. The Eye of Terror will repeat this pattern of attack until its HP drops below 3250, at which point it reveals its mouth and enters its second phase.
During its second phase, the Eye of Terror attacks in a pattern of charging 3-5 times consecutively, then spawning two Eggs of Terror at once instead of the previous one. The Eye of Terror also gains a slam attack that triggers when the player comes too close, creating a small sinkhole in the ground that lasts for 20 seconds, slowing down players who walk on it.
Strategy
The Suspicious Peepers spawned by the Eye of Terror take some time before they hatch, but killing them should always be a priority before they hatch, as they can quickly overwhelm the player.
Twins of Terror
The Twins of Terror, or The Twins, are two entities, Retinazor and Spazmatism, who spawn instead of the Eye of Terror if the Terrarium is fueled with one Nightmare Fuel before activating it. They have nearly identical attacks to the Eye of Terror but have 10,000 HP each, and both entities enter their second phase when they lose 7000 HP in total.
Unlike the Eye of Terror, the Twins do not regenerate HP if a night is skipped without spawning them. Once they have been summoned at least once, if a single night is spent without summoning them again, the Terrarium immediately enters its dormant state, and cannot be activated for another 15 days.
Retinazor retains the same attack patterns as the Eye of Terror, but prioritizes spawning Suspicious Peepers over charging. Its charges are slower than that of Spazmatism but its charging distance is longer. It starts with 10,000 health and it will enter its second phase when The Twins' combined health drops below 7,000 or immediately when Spazmatism is killed. In its second phase, Retinazor moves faster, gains the same sinkhole attack as the Eye of Terror, charges more often, and spawns even more Suspicious Peepers.
Spazmatism retains the same attack patterns as the Eye of Terror, but prioritizes charging over spawning Suspicious Peepers. Its charges are faster than that of Retinazor but its charging distance is shorter. It starts with 10,000 health and it will enter its second phase when The Twins' combined health drops below 7,000 or immediately when Retinazor is killed. In its second phase, Spazmatism moves faster, gains the same sinkhole attack as the Eye of Terror, charges more often, and spawns even more Suspicious Peepers. In its second phase, Spazmatism also will charge many more times consecutively before resting.
The Eye of Terror is referred to as the Eye of Cthulhu in Terraria, while the Twins of Terror in Terraria are just referred to as The Twins. In Terraria, Retinazor is spelled "Retinazer", and Suspicious Peepers are referred to as Servants of Cthulhu. The Twins are based off of the Eye of Cthulhu, with the aforementioned bosses being a mechanical and more difficult version of the Eye of Cthulhu.
The Twins of Terror have different attacks and appearances in Terraria.
Retinazer fires lasers whilst retaining distance from the player, while Spazmatism prioritizes on charging towards the player, occasionally spewing green, cursed flames. In Terraria, they never summon Suspicious Peepers (Servants of Cthulhu).
The Twins in Terraria appear differently, however. Both Retinazer and Spazmatism appear similarly to the Eye of Cthulhu, with the only difference being the color of their pupils. Retinazer's pupil is red, while Spazmatism's pupil is green.
On their second phase, Retinazer reveals a laser on its pupil, while Spazmatism reveals its fangs, similar to Don't Starve Together's Spazmatism.
The Twins in Terraria are always connected by a long tendril, unless separated from each other far enough. This is, however, absent in Don't Starve Together.
In Terraria, Servants of Cthulhu (Suspicious Peepers) are only spawned by the Eye of Cthulhu (Eye of Terror) but not by the Twins (Twins of Terror).
The Eye of Terror and Twins of Terror's drops are different in Terraria as well. The Eye Mask is referred to as the Eye of Cthulhu Mask and has no function, being a vanity helmet, while the Shield of Terror is referred to as the Shield of Cthulhu, drops from the Eye of Cthulhu (Eye of Terror) in Expert Mode instead of the Twins (Twins of Terror) and functions as an accessory, allowing the player to make a ramming dash.
Both the Eye of Terror and the Twins of Terror share the same soundtrack, which is an orchestral version of the Terraria soundtrack, "Boss 1".
The Twins in Terraria, however, has a different soundtrack ("Boss 2").
The Eye of Terror and Twins of Terror's summoning quote is from Terraria, which is the exact message when they are about to spawn naturally.
Attention: The following categories are only for the players look up the page based on their first impression, they have nothing to do with the actual categories/behavior/function/tags of these creatures
Attention: The following categories are only for the players look up the page based on their first impression, they have nothing to do with the actual categories/behavior/function/tags of these creatures
Attention: The following categories are only for the players look up the page based on their first impression, they have nothing to do with the actual categories/behavior/function/tags of these creatures
Attention: The following categories are only for the players look up the page based on their first impression, they have nothing to do with the actual categories/behavior/function/tags of these Mobs
↑Leira on Titter:"I haven’t been on social media much lately, life has been a lot! But I just finished my final day working on DST before taking a year long sabbatical. I’m so touched by how special my coworkers made me feel on my last day!!!"