The Twins can be summoned manually using a Mechanical Eye at night (7:30 PM to 4:30 AM). They also have a 1/10 (10%) 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.
The Mechanical Eye is a Hardmode item used to summon The Twins, the advanced and Hardmode version of the Eye of Cthulhu. It can only be used at night; using this item during the day will not spawn The Twins nor consume it.
Spider Staff is the best summoning choice because the spiders will latch on while they change forms, dealing hundreds of damage.
The Mechanical Eye can be obtained by killing Hardmode enemies.
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.
Queen Slime can be spawned in the Hallow or Underground Hallow by using a Gelatin Crystal, which is consumed upon use and immediately summons the boss. If used outside the Hallow, the boss will not be summoned and the Gelatin Crystal will not be consumed.
The Eye of Cthulhu can be summoned manually using a Suspicious Looking Eye at night (beginning at 7:30 PM in-game time). It also has a 1/3 (33.33%) chance of spawning automatically each night, if the following conditions apply: The Eye of Cthulhu has not yet been defeated in the current world.
The Fight. The Twins, as the name suggests, are two separate monsters, both of which must be defeated. They have a combined health of 43,000 / 64,500 , shared between them. Retinazer is distinguished by its red iris and that it fires lasers.
It is estimated that 1 in 250 natural pregnancies will naturally result in twins. While twin pregnancies can happen by chance, there are some factors that may increase your odds of having two babies at the same time.
Once you've defeated The Twins, it's time to move on to the other two Mechanical Bosses: The Destroyer and Skeletron Prime. Out of the three, The Twins are the easiest thanks to the simple boss arena and the ability to take it down with basic Hardmode weapons, or even weapons you have leftover from pre-Hardmode.
The Eye of Cthulhu is a Hardmode, post-Plantera yoyo which has a 1/3 (33.33%) / 5/9 (55.56%) chance to drop from Mothron during a Solar Eclipse. It is one of the few yoyos that can stay in the air indefinitely, and it has a reach of 23 tiles.
Moon Lord is the hardest boss undoubtedly within Terraria.
Queen Slime is one of the simpler bosses in the game, but that doesn't mean it's an easy fight. You may need to change your strategy depending on which difficulty you use and your equipment.
The Eater of Worlds is a pre-Hardmode Corruption-themed worm boss. It is summoned using Worm Food from within The Corruption or Underground Corruption, or by destroying 3 Shadow Orbs that spawn in Corruption worlds. It can be summoned at any time of day.
The Empress of Light can be summoned by killing a Prismatic Lacewing butterfly. These rare critters only spawn at surface-level Hallow at night, between 7:30 pm and 12 am. Luckily, the Lifeform Analyzer item can detect them, so Prismatic Lacewings can be easily farmed.
In childhood, fighting between twins on the deepest level is about the development of individuality. Contentiousness or power struggles provide the mini-steps that eventually create a unique sense of self for each member of the twin pair. Sometimes twins want the same exact “things” and they compete to win.
Titanium/Adamantite armor is recommended, it has a great set bonus and multiple buffs. If Titanium/Adamantite armor is not available, Mithril or Orichalcum armor will also do.