To put it into perspective, the "guaranteed reward point" (which is the base for ToT-esque events) system uses a value called "frequency" to control how odds are calculated based on the amount of points your character has accumulated. The lower the value, the better your odds at a drop, the lower your creature points. For Treasures of Tokuno that value was 44, for Blackthorn's Dungeon that value is 22, and for Treasures of Doom that value is 1. The way the GRP system works is that each creature you kill awards a pool of points based on their fame. That pool is distributed among players on the creatures "top attacker" list (which accounts for damage received, damage dealt, and damage healed). As you kill creatures you accumulate points, and the more points you have, the closer the chance of you getting an Artifact of Doom approaches 1 in 1. As mentioned in the patch notes, luck plays a role, and being hidden will reduce the amount of points awarded (this has been that way since Treasures of Tokuno).