Pearl Medallion
Artifact
White spells you cast cost 
less to cast.
It is a helping hand reaching out to the downtrodden, the acrid-sweet tang of burning incense during prayer, and the harmony of voices uplifted in unison. It is faith.
Daniel Ljunggren
Modern Horizons 3 (MH3)
• #294Rulings
If a spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell's total cost.
(wotc • 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.
(wotc • 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.
(wotc • 2023-07-28)
The cost reduction can apply to alternative costs such as flashback costs.
(wotc • 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.
(wotc • 2023-07-28)
Rulings
If a spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell's total cost.
(wotc • 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.
(wotc • 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.
(wotc • 2023-07-28)
The cost reduction can apply to alternative costs such as flashback costs.
(wotc • 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.
(wotc • 2023-07-28)