Exertion of the Necromancer

Tap target permanent you control and put a stun counter on it.
Choose a creature with mana value X from any graveyard, where X is the greatest power among creatures tapped this way.
Return the chosen creature to the battlefield under your control.
Overload {b} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")