Ubbo-Sathla, Tome Keeper

Devoid
When Ubbo-Sathla, Tome Keeper enters the
battlefield, create a Legendary Tablet of the
Gods token with "{t} Pay X life and sacrifice
Tablet of the Gods: search your library for a card
with mana value X, reveal it and place it in
your hand. Activate this ability only as a sorcery
and only on your turn"