Dark Ritual is a game function that acts as a soft reset; heroes are all returned to level 0, but achievements, magic bottles, gilds, equipped artifacts, Hearts, Emerlands, Hero Shards and craft equipments are untouched. Upon using Dark Ritual, the player receives 1 Hero Soul for every 200 hero levels purchased, and more for beating Soul Bosses whenever they appeared during the now closed game cycle.
Dark Ritual is unlocked from Brath the Merciless at hero level 125.
Please note: if you send Brath to mines the ritual will not be available until he returns.