Pearl Medallion

2023-07-28 If a spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell's total cost.
2023-07-28 If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben's ability), apply those increases before applying cost reductions.
2023-07-28 The ability can't reduce the amount of colored mana you pay for a spell. It reduces only the generic mana component of that cost.
2023-07-28 The ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
2023-07-28 The cost reduction can apply to alternative costs such as flashback costs.

Card is in preconstructed decks:

mtg.wtf