The Annihilator

The Annihilator is a Hardmode Boss and is part of the Steam Trio bosses.

Spawn
The Annihilator, like most other bosses, does not spawn on its own and requires the player to summon it with the Steam-O-Vision.

Behavior
The Annihilator behaves similarly to Brain of Cthulhu, but the differences are that he doesn't teleport around. It spawns many new minions as the health decreases of milestone and becomes more aggressive.

Phase 1

 * It spawns Mechanical Spiknator when hitting the boss, that behaves similarly to Spike Balls. It also spawns Mechanical Charger in which it follows you around, like Demon Eyes.
 * Unlike the Brain of Cthulhu, The Annihilator does not spawn with minions. Instead, it spawns many types of minions to attack the player the lower its health gets.
 * Upon reaching 65% health, it enters its second phase, spawning more minions at each health milestone.

Phase 2

 * At each health is decreasing, the mirrors become more visible.
 * Enemies spawned by The Annihilator will become mirrored when the health starts to go down:
 * After reaching 2nd phase, it will then summon Mechanical Copter, which will rapidly fire bullets like other guns.
 * Upon reaching half health, it will spawn Mechanical Mimic that acts as a mimic.
 * Upon reaching 45% health, it will spawn Mechanical Creepers, which follows the player itself.

In Expert Mode

 * The Annihilator and all minions will now inflict Steamy debuff in 4 seconds.
 * Following the 2nd phase, the boss will now inflict Electrified debuff in 2 seconds.
 * Spawns more minions as the health decreases.

Tips

 * Like Brain of Cthulhu, the only way to know which one is real or fake is to move slowly towards one of the illusions. If the illusions spread out, then the brain is at the other side. However, if the illusions close in that the player is getting nearer to the brain making it easier to tell.
 * Daedalus Stormbow is an excellent option to fight, as the arrows fire down towards the sky and easier to dodge the projectiles.