Ba'ul, Diligent Soulseeker

Double strike, vigilance, indestructible
Whenever a creature you don't control dies or is exiled from the battlefield, put a soul counter on Ba'ul.
Whenever you remove one or more soul counters from
Ba'ul, put that many +1/+1 counters on Ba'ul.
{x}{u}{r}, {t}, Remove X soul counters from Ba'ul: Exile
the top X cards of your library. You may play those cards for as long as Ba'ul is on the battlefield.
{x}{b}{r}, {t}, Remove X soul counters from Ba'ul: Ba'ul deals twice X damage to target creature a