What insolence! That flesh-thing not only defiled a branch of my laboratory and destroyed my prototype, but it made light of Finger of Death! The instant-death spell that drives magic apprentices to study the dark arts, dark apprentices to become necromancers, and necromancers to become liches!
After a lifetime of study and experimentation, I wasn't even halfway to completing it. The thought of a living being being unharmed by it is an insult to magic. And what happened after!
To this end, I study the many instruments in my central laboratory. Detectors, signature sensors, range-finders, recorders... the data is all over the place. The spell clearly hit that flesh-thing, but the effect didn't activate. How!? Then, the spell it used against me, it is unrecognizable.
In my decades of study, I haven't neglected the threat of magic resistance. There exist magical equipment, support spells, even skills that provide many ways of resisting magic. I've studied them well enough to enchant such equipment myself, were it not an offense to my craft.
There is a common weakness to these methods: they are activated by magic, not its secondary effects. This problem is infrequent enough that few spells try to be quite so indirect as to not contact the opponent with magic at all. But, whatever its rarity, that problem has come to my door.