Sabboth, the Relentless

Whenever a creature you control dies, each other creature you control gets +X/+X until end of turn, where X is that creatures power.
Cumulative Upkeep-Sacrifice a creature. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever Sabboth, the Relentless leaves the battlefield, exile your graveyard.