Llahsram, the Creator

Eminence — Whenever another legendary
creature enters the battlefield under your control,
if Llahsram is in the command zone or on the battlefield, put a lore counter on that creature.
Whenever a creature you control with a lore
counter on it dies, create a clue token.
Whenever you sacrifice a clue, roll a d20.
On a 16+, create a treasure token.
And you get a backstory!