Wall of Steel

The Wall of Steel is a boss that can be spawned in the Underworld by letting a Mechanical Guide Doll fall into lava after Hardmode has been unlocked. It is a stronger, mechanical version of the Wall of Flesh. Once the doll has fallen into lava, the Guide will die, and the Wall of Steel will awaken.

Stats

 * 4,000 (eyes)
 * 6,000 (mouth)
 * 10,000 (Body)
 * 104 Damage
 * 94 Damage (laser)
 * 100% KB resistance

Battle
Like the Wall of Flesh, the Wall of Steel has a mouth and two eyes, the eyes representing the Twins and the mouth representing the Destroyer. The mouth spawns out Probes as a replacement to The Hungry II and Skeletron Prime arms that function the same way as the boss as a replacement to The Hungry. The eyes must be shot at first. Once they die, Probes and Prime Arms will stop spawning out of the mouth. Before the eyes' death, the rest of the body is indestructible. When the eyes die, the mouth will start breathing fire at the player. The rest of the body will be covered with spines that inflict damage to any player that attacks it with a melee attack. Once the mouth dies, the entire body will begin moving faster and also be open to attack. Once the body is destroyed, the drops from the Wall of Steel will spawn inside a square of Demonite/Crimtan Bricks.

After the defeat of the Wall of Steel, it will drop 4 Flags. Once you use one, a message will appear saying "The ancient spirits of light and dark have come to wage war!" This marks the beginning of War Mode. Three types of ore will also spawn: Cryocite Ore in the Snow biome, Verdantite Ore in the Jungle and Aridite Ore in the Desert.

Drops
Only one of the following will drop Only drops in Expert Mode
 * Coins
 * Greater Healing Potions
 * Crimson Emblem (Only if the world has Crimson)
 * Corruption Emblem (Only if the world has Corruption)
 * 10-20 Soul of Fight
 * Blue Flag
 * Red Flag
 * Pink Flag
 * Gold Flag
 * War Pickaxe (12.5%)
 * Sun Waraxe (12.5%)
 * Shadow Blade (12.5%)
 * Steel Gun (12.5%)
 * Treasure Bag (Wall of Steel)