Rhoren, Monster's Bane

When any target Horror, Beast, Demon, or Dinosaur Creature greater than 3/3 enters the battlefield, Rhoren, Monster's Bane is +X/+X
(X = that Creature's power/toughness) until that Creature is in the Graveyard or until a stronger Creature is played.
After target Creature is destroyed, sacrifice Rhoren with a countdown timer of 6.
Rhoren found redemption and infamy saving civilians from terrible beasts and horrors, but at great cost to themself.