Deadly Outbreak

When Deadly Outbreak enters the battlefield, put a -1/-1 counter on target creature.
During your upkeep, put a -1/-1 counter on each creature with a -1/-1 counter on it. For each -1/-1 counter placed this way, put a -1/-1 counter on target creature with no -1/-1 counters on it.
When there are no creatures on the battlefield, sacrifice Deadly Outbreak.