The grim reaper

Indestructible
The grim reaper's power and toughness is equal
to the number of creatures in all graveyards.
Devotion to death - As long as there's no five black creatures at least in all graveyards, The grim
reaper isn't a creature.
Exile a creature card from a graveyard, you can
add its convert mana cost to your mana pool in
black mana only.