This is tricky one, i think you would have to change entire spell system around and change Storage Values on player when he uses attack spells (spells what do damage or debuff monsters)
And then in creaturescripts you do scripts what says something like this: StorageValue "this" doesn't damage, StorageValue "that" doesnt slow, etc.
And finally add that creaturescript to the monster.
But this is how i would do it, perhaps there is easier solution.
(i wont provide you with script example, because it would take me day or 2 to make it work, not skilled scripter here)