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 D20
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This article is a D20 reference page
The System Reference Document is a comprehensive toolbox consisting of rules, races, classes, feats, skills, various systems, spells, magic items, and monsters compatible with the d20 System version of Dungeons & Dragons and various other roleplaying games from Wizards of the Coast.
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Knock-Down [General]
Prerequisites
Base attack bonus +2, Improved Trip, Str 15.
Benefit
Whenever you deal 10 or more points of damage to your opponent in melee, you make a trip attack as a free action against the same target.
System Reference Document -> Feats