Obscura Ascendancy

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.

Streets of New Capenna Promos

Streets of New Capenna

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.

If there are no soul counters on Obscura Ascendancy, its ability triggers if you cast a spell with mana value 1. If there is one counter, its ability triggers if you cast a spell with mana value 2, and so on.

Obscura Ascendancy's triggered ability has an “intervening ‘if'” clause. This means that it checks the number of counters both when the ability triggers and when it resolves. Notably, this means that casting two instants in a row with mana value 1 will never cause a player to create two tokens or put two counters on Obscura Ascendancy.