3e SRD:Stand Still
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Stand Still [Psionic]
Prerequisite: Str 13+, reserve power points 1+.
Benefit: When a foes movement would otherwise grant the character an attack of opportunity, the character may give up that attack and instead attack the foe prior to the foes actual movement. This is akin to a readied action, but Stand Still doesn't affect the characters initiative count or actual readied actions, if any. The foe must succeed at a Fortitude save against a DC equal to 10 + the damage dealt, or be unable to move into or out of the area the character threatensessentially, this ends the movement of a foe who is closing, and prevents any movement of a foe who is fleeing (if the character is normally allowed an attack of opportunity against the fleeing foe). Since the character uses the Stand Still feat in place of his or her attack of opportunity, the character may only do so a number of times per round equal to the number of times per round he or she could make an attack of opportunity.
Normal: Attacks of opportunity occur after a foe has already moved within the area a character threatens; thus, a character is unable to affect their movement with an attack.