Blighttree of Shared Pain

Cumulative Upkeep - You get a poison counter.
At the beginning of each of your end steps, you may have target player get X poison counters where X is equal to the number of poison counters you gained that turn.
{b}{b}{b}, {t}, Sacrifice Blighttree of Shared Pain: Remove all poison counters from each player and put that many -1/-1 counters on each creature.