You can make yourself a little more vulnerable to larger creatures in order to land a devastating blow.

Prerequisites: Goblin, Halfling, Dwarf or Gnome level 3

Benefit: You can choose to take a 2 penalty to AC to gain a +2 precision bonus on melee damage rolls against creatures one size categories larger than you. When your base attack bonus reaches +4 and every 4 levels thereafter, the penalty increases by 1 and the damage bonus increases by 1. You can only choose to use this feat when you declare that you are making an attack action or a full-attack action with a melee weapon. The effects last until your next turn.