I really liked this ability, arguably one of the most effective in Magister tree, sadly it has one major drawback.
There's no way of telling which creatures it affects unless you click on them one by one and check their information box.
It would vastly improve it's usefulness if maybe something akin to the curse spell animation appeared over their heads once the creatures got this debuff. That way you can target such creatures for individual spells, instead of wasting spellpoints on monsters that will most assuredly make the save.
For those who don't know, it gives -5 to specific saves (for your school) for 10-20-30 seconds, depending on the tier.