Leviathan, Spawn of Scylla

When Leviathan, Spawn of Scylla enters the battlefield, you may search your library for a card called Scylla, Master of Messina and put it on the battlfield tapped. Then shuffle your library.
Whenever a Hydra enters the battlefield, put a
+1/+1 counter on it and you gain one life.
{1}{b}{u}, Sacrifice a creature: Create a X/X black
Hydra creature token where X is the sacrificed creature's power.