Ruins Rebuilding

Each creature you control with a -1/-1 counter gets a +1/+1 counter for each -1/-1 counter on it.
Flashback, {w}{4} (You may cast this spell from your graveyard, then remove it from the game)
Creatures target player controls are sacrificed, then returned to the battlefield, their enter the battlefield abilities activated and they enter the battlefield with the same amount of
-1/-1 counters on it that it had.
Once this ability is used, sacrifice ruins rebuilding.