Sanctum Prelate
Creature — Human Cleric
Oracle Text
As this creature enters, choose a number. Noncreature spells with mana value equal to the chosen number can't be cast.Rulings (2)
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Wizards of the CoastFor spells with
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 
couldn't be cast with X equal to 2, but it could be cast with X equal to any other number.
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Wizards of the CoastEffects that increase or reduce the cost to cast a spell don't affect that spell's mana value.