Cthulhu

When Cthulhu enters the battlefield all players
must either lose health equal to the number of
madness counters on themselves and creatures
they control or discard cards from the top of their
library equal to the number of madness counters
on themselves and creatures they control times
two.
All Cultist, Monstrosity, Merfolk, Leviathan, and Octopus creatures you control gain islandwalk.