Cthulhu, From Eternities

Islandwalk
Leviathan, Octopus, Serpent, and Kraken creatures
cost {2} less for you to cast as long as Cthulhu is in
the command zone.
{5}, Sacrifice Cthulhu: Search your library or graveyard for a Leviathan, Octopus, Serpent, or
Kraken creature and put it onto the battlefield. If
you searched your library this way, shuffle it.