Bane: Can I apply multiple bane special abilities to the same weapon? If so, do their effects stack?
You can apply multiple bane special abilities to the same weapon. For example, you can have a +1 dragon- and fey-bane longsword, which has an increased enhancement bonus and damage against dragons and against fey.
If you have multiple bane effects on a weapon and attack a creature against which more than one bane applies (such as a chaotic- and evil-outsider bane weapon used against a demon), the effects do not stack: the weapon's enhancement bonus is only +2 higher than its actual enhancement bonus, and it only deals +2d6 points of damage against that opponent.
(Compare to fighter weapon training or ranger favored enemy bonuses, both of which say you use the highest bonus if more than one bonus applies.)