cr:6.4.10i

A fixed-prevention effect is a prevention effect that acts as a one-off effect. It prevents a specific amount of damage from an event that activates it. Fixed-prevention effects are typically written in the format “[CONDITION], prevent [PREVENTION].” After a fixed-prevention effect prevents damage, any remaining prevention amount is not used to prevent a subsequent damage event.

Example: Dissipation Shield has the text “Instant – Destroy this: The next time you would be dealt damage this turn, prevent X of that damage, where X is the number of steam counters on Dissipation Shield,” which is a fixed-prevention effect that modifies to the next event that would deal damage to your hero this turn but does modify any additional damage events that turn.