The black orb does not work on the new resistance effect. It only removes standard immunities, as well as the resistance chance of dwarves and crystal dragons (whose abilities have not changed). Yes, Thorgrim can achieve 100% resistance – in that case, the opponent's magic power will always be 1. But he will still be able to cast berserk (which does not depend on magic power) and a few other similar spells, and he can also increase the duration of spells by using treasure artifacts that provide a bonus to spell duration. So, it's unlikely that this can be called a complete inability to cast spells. However, it has already been discovered that Thorgrim's special ability is not working right now. :) But this bug will be fixed soon.