Exxo Avalon/Wall of Steel

"Black white gray."

The Wall of Steel is a hardmode boss. It is the trigger boss in Exxo Avalon. To summon it, you must drop a into lava once Golem has been defeated, and it can only be fought in The Underworld.

Behavior

 * It acts similarly to the Wall of Flesh. Upon spawning, it will also have a multitude of Mechanical Hungries. When the Wall of Steel is above 1/3 HP, it will shoot bouncing cursed fireballs and a spread of cursed flame balls from the top eye, and fire lasers from the bottom eye.
 * Dropping the boss to 1/3 HP will change its AI; it will charge a large, high-damage laser and fire it from the center aperture. It will also shoot cursed flamethrowers from the top eye.

Aftermath
Upon death, Superhardmode begins. The main changes are:
 * ,, , , and are generated.
 * can be destroyed with or stronger.
 * Various new enemies spawn.
 * The biome is generated.

Trivia

 * The Wall of Steel used to be a very widely talked-about idea for mods, although there was never an actual addition of this boss until now.
 * This boss was originally purposed as the Superhardmode trigger for the now paused Exxo Avalon: Origins for Terraria 1.3.
 * Unlike the Wall of Flesh, its top and bottom "eyes" do not look at the player.