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(32) Although not expressly forbidden, the practice of using stealth or invisibility to gather the treasure of random exploreable areas without actually defeating the monsters is in most cases frowned upon. If your character(s) engage(s) the monsters, fail and are unable to defeat the foe, feel free to consult with a DM if it would be appropriate to attempt to use stealth and trickery to plunder the area.

If the AB bonus is applied to the weapon, then it will pierce DR up to that number regardless of enhancement.

I noticed this myself when I tried to use the spell, but contributed to the AB increase from my Casting level preventing it from applying.