i wouldn't mind seeing a chart created for what the fumble does. like, if you fail the above Dex check, roll a 20 again to see what happens. on the high end (16-20?), it could be as simple as "you lose your weapon" or "ranged weapon is rendered useless (bow string breaks, etc.". the mid range (8-12?) could be dangerous, "you provoke attacks of opportunity from anyone who threatens your area". the lowest could be "you automatically strike an ally, or yourself if none are in weapons range (no to-hit roll required)"