Silent Death (Fallout Supplement)
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SILENT DEATH [Combat]
You're adept in the art of stealth attacks.
Prerequisite: Dexterity 17, 10 ranks in Move Silently and Hide, Stealthy
Benefit: If you attack someone from behind while successfully undetected, you deal an additional 1d8 of damage for every 3 levels you possess.
Special: This damage is not multiplied by critical hits.