Nurgle, the Rot Father

Whenever a creature with a -1/-1 counter on it dies, put a Plague counter on Nurgle, the Rot Father.

Nurgle, the Rot Father is not a creature unless there are seven or more Plague counters on it.

Creatures you control have Wither.

If there are seven or more Plague counters on Nurgle, the Rot Father, creatures you control have Undying.