The Jailer, Tormentor

Whenever a creature you control deals combat
damage to a player, put a soul counter on
The Jailer.
At the beginning of your end step, if The Jailer
has three or more soul counters on it, you may transform it.
{b},{t}, Sacrifice three creatures: Create a 5/5
Demon creature token with flying and "When this creature dies, its controller loses 5 life."