Blood Magic Ritual

Pay 1 life: add one mana of any color to your mana pool, then put one Possession counter on Blood Magic Ritual.
At the beginning of your upkeep, if Blood Magic Ritual has five or more Possession counters on it, sacrifice it, then put an X/X blue and black Abomination creature token onto the battlefield under your control, where X is the difference
between your starting life total and your current life total.