It lowers the opponents magic level by the damage you hit them for. However, there was a rumour the max it can lower it by is 7, even if you hit like a 13. Well, last time that was it. nope i heard its just a straight damage for magic lvl spec-no cap involved. i think the max hnit is about 20 too but for a full special bar you have to decide if its worth it (mainly only applies to duelling) cos although you may have taken down their mage they can still range you with a damaging speical like mage short or dds u 4 times. its ur choice but depends on the duel rules, ur skill and ur lvls.