Originally Posted by Djinn_In_Tonic
If I understand correctly, this item is incredibly overpowered, allowing you to inflict a 5d6 bonus or a -15 penalty to a d20 roll up to twice a day for a mere 7,200 gp.
So far as I understand it, it's subtract and
add--you add a +5d6 bonus and subtract a -15 penalty, generating a modifier between +15 and -10. If you use it on an ally you could get a penalty, and if you use it on an enemy you could get a bonus.
Whether that brings the cost down to 7200gp is up to interpretation, but I'd say something that swingy would be around 7500gp, with a possible boost for being usable multiple times on the same roll.