Katil, Catharsis of Mutation

Whenever a creature enters the battlefield, you
may pay {1}. If you do, put a +1/+1 counter on
that creature and it becomes a mutant in addition
to its other types.
Whenever a mutant control dies, you may exile it.
If you do, proliferate.
"Brah makes all yer stuff into mutants nad puts
counters on things AND has proliferating effects. Braaaaaah" -Gideon, Planeswalker