Nezumi, Forced Mutation

Planeswalker Mutate: {u}{b}{r} (If you cast this spell for its mutate cost, put it over or under target planeswalker creature you own. They mutate into the planeswalker on top plus all abilities from under it. It isn't a creature)
Mutate {u/b}{u/b}
As long as Nezumi, Forced Mutation is not a planeswalker, he has deathtouch and gets +1/+1 for each loyalty on him.
Whenever Nezumi, Forced Mutation mutates, put a loyalty counter on him.