Haunter

Evolve 12 - At the beginning of your upkeep,
gain 1 Experience Counter. Then, if you have
12 or more Experience Counters, Exile Haunter,
and put Gengar onto the battlefield from the
Command Zone. You may pay {p/b} once per turn
to gain 1 Experience Counter.
Flying, Shadow
{b}{b}: Haunter gains a lifelink until end of turn.
{b}{b}{p/b}: Put a -1/-1 Counter on target creature.
It cannot attack or block this turn.
Mutate {3}{b}{b}