Rule 615.10

Some prevention effects generated by static abilities refer to a specific amount of damage—for example, “If a source would deal damage to you, prevent 1 of that damage.” Such an effect prevents only the indicated amount of damage in any applicable damage event at any given time. It will apply separately to damage from other applicable events that would happen at the same time, or at a different time. Example: Daunting Defender says “If a source would deal damage to a Cleric creature you control, prevent 1 of that damage.” Pyroclasm says “Pyroclasm deals 2 damage to each creature.” Pyroclasm will deal 1 damage to each Cleric creature controlled by Daunting Defender’s controller. It will deal 2 damage to each other creature.

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