Planar Symbiote

Vigilance, Lifelink
Symbiote (when this creature dies, return it to the battlefield underneath target creature you control, it becomes melded. At the beginning of your upkeep, put a knowledge counter on the melded creature. When the melded creature leaves the battlefield, symbiotes are put into the graveyard)

Melded creature gains symbiote. Each time a knowledge counter is put on this creature, gain 1 ability from the symbiotes medled to it.