War Mode

War Mode is a mode unlocked after beating the Wall of Steel and using one of the 4 Flags dropped by it. Once unlocked, it is permanently activated for that world. It brings with it much stronger Tools, monsters, bosses and events.

For War Mode to start, you must use one of 4 Flags dropped by the Wall of Steel. These flags are the Blue (Corruption), Red (Crimson), Pink (Hallow) and Gold (Confection) flags. Whatever flag you use, that will be the side you fight for. After using one flag, the others disappear from your inventory.

The side you pick decides what monsters will attack you. The monsters of your alternate biome (ex. Corruption vs. Crimson) will attack you before any other monsters. The monsters of your opposing biome (ex. Corruption vs. Hallow) will attack you, but tend to the monsters they are fighting first. The monsters of the biome that you chose will fight for you if anything attacks you, and the monsters from the biome with no relation to you (ex. Confection for Corruption) will simply ignore you.

Mobs
When War Mode is activated, many new mobs will start spawning.
 * Possessed Eye (night)

For the full list, go Here 
 * War Slime (underground, cavern)
 * Centipede (underground)
 * Millipede (cavern, underworld)
 * Cave Crawler (cavern)
 * Enchanted Bow (night)
 * Anubis (desert)
 * Tiger (jungle)
 * Gravitant (moon biome)
 * Teleporter (moon biome)
 * Bloody Slime (crimson)
 * Corrupted Wolf (corruption)
 * Dragon (hallowed)

Biomes

 * The Judgement
 * The Necro
 * Moon Biome
 * The Reaped