Sanctum Prelate

Aug 23, 2016 · For spells with {X} in their mana costs, use the value chosen for X to determine if the spell's mana value is the chosen number. For example, if the chosen number is 4, a noncreature spell with mana cost {X}{R}{R} couldn't be cast with X equal to 2, but it could be cast with X equal to any other number.

Aug 23, 2016 · Effects that increase or reduce the cost to cast a spell don't affect that spell's mana value.