Goglomog, Devouring Tide

Islandwalk
Whenever an opponent casts a spell, put a +1/+1 counter on Goglomog, then put a 1/1 blue frog
knight creature token with Islandwalk onto the
battlefield tapped.
{3}{g}{u}{b}, Sacrfice three frogs: Goglomog gains
double strike until end of turn.