Omen of Leshrac

Sacrifice Omen of Leshrac: Return a card
from your graveyard or a card you own in
exile on the bottom of your library.
Bolas' mask returned to Nether Void, the Shard
of the Twelve Worlds came back to instability
thus unsealing the Madaran Rift and releasing
the languishing nightmares that slept inside of it
in the darkest depths of Voda Sea.