Three Blades of Obzedat

At the beginning of your upkeep, exile Three Blades of Obzedat, then flip a coin. On heads, return it to the battlefield with a +1/+1 counter on it. On tails, return it to the battlefield with a -1/-1 counter on it.
If Three Blades of Obzedat has a -1/-1 counter on it, creatures you don't control get -1/-1.
If Three Blades of Obzedat has a +1/+1 counter on it, creatures you control get +1/+1