Possible Spoil, depending on what you consider spoil.
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While looking for a Spell Immunity scroll, I noticed something that Ribald sells unlimited quantities of Ring of Air, which casts Imp Invis 1x per day, for a pittance, a couple k a pop, or something like that. If you really felt so inclined, you could fill a gem bag with these puppies, and pass them around as needed.

<font color=white> This is common knowledge ;) .... </font>