I've always wanted transmuters to get a spell the causes the target to lose control of a limb. Call it limb spasm. If cast on a leg it makes the victim move in a randomn direction whenever they try to move or make them fall to one knee(one round lag). If cast on an arm(here's the fun part) it makes them punch themselves silly. Almost like Ash's bad hand, from Army of Darkness.

P.S. You should change fumbles emote to something like;
Vizzagoth utters "fumbleword" and makes a snapping gesture.
Your hand muscles spasm in pain and you drop your weapon to the ground.

That which does not kill us,
makes us stronger.