shadowforge reaper

at the beginning of your upkeep sacrifice each creature your control with a -1/-1 counter on it unless you sacrifice a land for each of those creatures
{x}{x}{b} target creature gets -x/-x until end of turn. if a creature would die this way return it to the battlefield under your control with a -1/-1 counter on it. shadowforge reaper gets -2/-2 until end of turn, activate this ability only once each turn.