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Source: Player's Handbook

Description: You can fight with a weapon in each hand with greater ease.

Prerequisites: DEX 15

Required for: Greater Two-Weapon Fighting, Hand of Osano-Wo, Improved Two-Weapon Fighting, Prayer's End, Two-Weapon Defense

Your penalties on attack rolls for fighting with two weapons are reduced. The penalty for your primary hand lessens by 2 and the one for your off hand lessens by 6.

Special

A 2nd-level ranger who has chosen the two-weapon combat style is treated as having Two-Weapon Fighting, even if he does not have the prerequisite for it, but only when he is wearing light or no armor. A fighter may select Two-Weapon Fighting as one of his fighter bonus feats.