"These halls are sacred. You will be silent."

Sanctum Prelate

As this creature enters, choose a number.
Noncreature spells with mana value equal to the chosen number can't be cast.

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"These halls are sacred. You *will* be silent."

Conspiracy: Take the Crown

As Sanctum Prelate enters the battlefield, choose a number.
Noncreature spells with converted mana cost equal to the chosen number can't be cast.

Effects that increase or reduce the cost to cast a spell don't affect that spell's mana value.

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.