Accumulative Sludgemorph

Whenever Accumulative Sludgemorph attacks or blocks, put a +1/+1 counter on it, then it gains
all abilities as well as power and toughness of another creature on the battlefield. Accumulative Sludgemorph gains that creature's type in addition to Accumulative Sludgemorph's other creature types.
It adds its victims to its collection, much like a dragon adds on treasure to its hoard.