Gonti, Stealer of the Dead

Deathtouch
Whenever Gonti, Stealer of the Dead enters the battlefield exile four cards face down at random
from target opponent's graveyard. Choose one of
those four cards and put it in a separate pile face
down.
You may look at and cast chosen cards for as long
as it remains exiled, and you may spend mana as
though it were mana of any type to cast that spell.