Skull Collector

Whenever a creature an opponent controls dies,
put a +1/+1 counter onto Skull Collector.
As long as Skull Collector has 4 or more power, it
has menace.
As long as Skull Collector has 6 or more power, it
has trample.
As long as Skull Collector has 10 or more power,
it has hexproof and lifelink.