Ruby Medallion
Artifact
Red spells you cast cost 
less to cast.
It is the warm glow of the setting sun at journey's end, the scent of the evening meal crackling over a fire, and the cacophony of a raucous song shared over tankards of mead. It is freedom.
Daniel Ljunggren
Modern Horizons 3 (MH3)
• #295Rulings
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)
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)
Rulings
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)
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)