Irida, Giant Kelpkeeper

At the beginning of your upkeep, if Irida, Giant Kelpkeeper was cast last turn, you may pay {x}. If you do, search your library for a Leviathan
card with converted mana cost equal to or lower
than X and put it onto the battlefield tapped
under your control.
Eons ago, Irida was born from the forest of kelp on the bottom of the ocean. After her, many other leviathans hatched in it, under her care.