Forbidden Ritual

{x}{b}: At the beginning of your upkeep, you may exile X creatures you control. If you can't, sacrifice this enchantment. Create X Petrified Soul tokens and put X Ritual counters on this enchantment.

{t}, {3}{b}, Remove three Ritual counters: Return a Legendary creature card with only black energy symbols in its cost from your graveyard to the battlefield. This triggers its resurrection effect. This card does not untal at your next unkeep.