Some effects state that damage “can’t be prevented.” If unpreventable damage would be dealt, any applicable prevention effects are still applied to it. Those effects won’t prevent any damage, but any additional effects they have will take place. Existing damage prevention shields won’t be reduced by damage that can’t be prevented.
January 25, 2019 · Ravnica Allegiance
Some effects state that damage "can't be prevented." If unpreventable damage would be dealt, any applicable prevention effects are still applied to it. Those effects won't prevent any damage, but any additional effects they have will take place. Existing damage prevention shields won't be reduced by damage that can't be prevented.
July 8, 2017 · Hour of Devastation
Some effects state that damage “can’t be prevented.” If unpreventable damage would be dealt, any applicable prevention effects are still applied to it. Those effects won’t prevent any damage, but any additional effects they have will take place. Existing damage prevention shields won’t be reduced by damage that can’t be prevented.
November 11, 2016 · Commander 2016
Some triggered abilities trigger when damage that would be dealt is prevented. Such an ability triggers each time a prevention effect is applied to one or more simultaneous damage events and prevents some or all of that damage.