Maelstrom Muse
Creature — Djinn Wizard
Flying
Whenever this creature attacks, the next instant or sorcery spell you cast this turn costs 
less to cast, where X is this creature's power as this ability resolves.
She's an inspiration to everyone, even herself.
Michele Parisi
Rulings
To determine the total cost of a spell, start with the mana cost or alternative cost you’re paying, add any cost increases, then apply any cost reductions (such as that of Maelstrom Muse’s triggered ability). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.
(wotc • 2021-04-16)
Maelstrom Muse’s cost reduction can reduce only generic mana in a spell’s total cost. It can’t reduce colored mana requirements.
(wotc • 2021-04-16)
Rulings
To determine the total cost of a spell, start with the mana cost or alternative cost you’re paying, add any cost increases, then apply any cost reductions (such as that of Maelstrom Muse’s triggered ability). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.
(wotc • 2021-04-16)
Maelstrom Muse’s cost reduction can reduce only generic mana in a spell’s total cost. It can’t reduce colored mana requirements.
(wotc • 2021-04-16)