cr:6.4.10h

If an effect states that a prevention effect cannot prevent the damage of an event, the prevention effect still applies to the event but its prevention amount is not reduced. Any additional modifications to the event by the prevention effect still occur.

Example: Enchanting Melody has the text “If you would be dealt damage, destroy this to prevent 4 of that damage.” which is a fixed-prevention effect with an additional modification that destroys the source. If a damage event occurs that cannot be prevented, Enchanting Melody’s prevention effect applies once to the event but does not reduce the damage dealt and Enchanting Melody is still destroyed.

Example: Steadfast has the text “Prevent the next 6 damage that would be dealt to your hero this turn by a source of your choice,” which is a shielding-prevention effect. If a damage event occurs that cannot be prevented, Steadfast’s prevention effect applies once to the event but does not reduce the damage dealt and does not have its prevention amount reduced. As such will still be able to prevent a total of 6 damage from the source after the event.