Since muters have to do with anatomy and nerves...Why not have a forget type affect? IE Disrupt brain (or something to that effect) in which case either a forget affect (I'm not to keen on this as I am the next...) Or a scrambling of there uses. For example..You cast it on a warrior. That warrior in turn enters bash onto his screen. As an affect that checks a percentile of the disrupt spell he may end up doing something totally random like feinting or dirt kicking. And Enhance brain paramters. Which would basically do like berserk for warriors offensive abilities, raises the percentile of each ability like 5 percent and on up. Example...
af:
Enhance paramaters affected for 4 hours.

skill jab 85%(90%)

Just another idea...