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Assassin's shroud
assassin feature

At-Will (Special) ✦ shadow

Special: A character can use assassin's shroud only on his or her turn, and only once per turn.

Target: one creature within the burst that the user can see

Effect: The target is subject to the user's shroud. If the target is already subject to the user's shroud, it is subject to an additional shroud, to a maximum of four. Shrouds end when invoked by the user, when the user uses assassin's shroud against a different enemy, or at the end of the encounter.

The user can choose to invoke all shrouds on a target before making an attack roll against the target. If so, that attack deals additional damage, which does not benefit from bonuses to damage rolls. If the attack hits, the additional damage is 1d6 per shroud. If the attack misses, the additional damage is calculated as though one fewer shroud were invoked.
Level 11: 1d6 + 3 damage per shroud.

Level 21: 1d6 + 6 damage per shroud.

Assassin's shroud is an assassin power known by assassins with the Assassin's Shroud class feature. It allows the user to stack shrouds on a target to deal additional damage on a later attack.[Dr379:19]