As Foretold - Amonkhet - 42

Enchantment

Mana Cost: {2}{U}

At the beginning of your upkeep, put a time counter on this enchantment.
Once each turn, you may pay {0} rather than pay the mana cost for a spell you cast with mana value X or less, where X is the number of time counters on this enchantment.

Mythic · Amonkhet · #42 (AKH)

Illustrated by Tommy Arnold