True Mode

True Mode is a higher difficulty mode activated with the Sigil of the Corrupted One. The sigil only drops once per world, obtained from the Moon Lord in expert mode. The item can only be used in expert mode and while there is no boss alive. Attempting to use it outside of these conditions does nothing and does not consume the item. The mode changes the behavior of the mod's post-Moon Lord bosses, and allows access to a few new items and mechanics.

Abaddon

 * Fires projectiles at higher speeds.
 * A second ring of Nightmare Souls orbit him in phase 4.
 * Minions also appear in phase 5.

Araghur

 * Serpent Aura debuff will change to Serpent's Curse debuff upon leaving the Flame Razed Forest for more than 10 seconds, changes back when reentering.
 * Serpent's Curse disables usage of healing potions, nullifies regen and decreases damage dealt
 * Araghur can fire a giant barrage of fireballs, indicated by a roar
 * If health goes below 20%, he will begin summoning Paradox Shadows, which appear faster the lower his health gets
 * Increased damage of all attacks

The Lost Siblings

 * The last active sibling in phase 1 will unleash a desperation move until defeated.
 * You have 4 minutes to beat Novaniel, and he buffs himself every minute that passes.
 * He will also begin inflicting Shattered Armor from empowerment 1 onward and Distorted Weapon from empowerment 2 onward.
 * When the timer runs out all players will die.

Other Changes

 * Nuba sells Exitum Lux armor and Lux Enhancement Shards after Abaddon, Araghur and The Lost Siblings have been defeated in True Mode. You will also have access to her special UI that allows you to enhance the armor with the shards.
 * The shards also start dropping from enemies after they have been defeated.