Nekomata

Unleash (You may have this creature enter the battlefield with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)
At the beginning of your your upkeep you may have Nekomata deals 4 damage to it's controller and Nekomata's controller sacrifices another creature. If not Nekomata deals 6 damage to to all creatures and players.