Come up with a spell that instantly kills the caster

Creating spells is a very dangerous and painstaking art. It requires lots of trial and error and even the best sourcerers have to wear five inch thick cotton armor bits when coming up with a new spell. One wrong gesture and you very well might blow yourself up or turn your sofa into something unnatural.

And all this is assuming that you can move your hands. Vocal-only spells are infinitely more difficult to create.