Obscura Ascendancy (SNC-BF)

Whenever you cast a spell, if its mana value is equal to 1 plus the number of soul counters on this enchantment, put a soul counter on this enchantment, then create a 2/2 white Spirit creature token with flying. As long as there are five or more soul counters on this enchantment, Spirits you control get +3/+3.