Ulthar, The Slime Dragon

Flying
Collective Mass (As this creature enters the battlefield, you may sacrifice it to another Ooze
you control, if you do, add all abilities, power,
and toughness of the Ooze that was sacrificed
onto the Ooze that was sacrificed to)
Whenever you sacrifice an Ooze, put that many
+1/+1 counters on this creature.