roiling horror's power and toughness are each equal to your life total minus the life total of an opponent with the most life.
suspend x—xbbb. x can't be 0. (rather than cast this card from your hand, you may pay xbbb and exile it with x time counters on it. at the beginning of your upkeep, remove a time counter. when the last is removed, cast it without paying its mana cost. it has haste.)
whenever a time counter is removed from roiling horror while it's exiled, target player loses 1 life and you gain 1 life.