Vixen, Crystalline Icefox

Mutate {s}{s}{s}{s} (If you cast this spell for its mutate
cost, put it over or under target non-Human creature
you own. They mutate into the creature on top plus all
abilities from under it.)
Whenever this creature mutates, choose a kind of counter at random that the creature on top
doesn't have on it from among flying, double
strike, deathtouch, hexproof, lifelink, menace,
reach, trample. vigilance, prowess, and +1/+1.
Put a counter of that kind on this creature.