Obscura Ascendancy [Streets of New Capenna Prerelease Promos]

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