Heptet, Sister of Remorse

Wither
When an opponent fails to pay tribute, that
opponent sacrifices a creature and you create a
1/1 black Demon Spirit Token with Wither.
{b}{b}{b}{b}{b}{b}: Target Demon you control gains Undying until end of turn. Costs {b} less for each
-1/-1 counter on creatures your opponents
control.