And its variants.

I created one that inflicts 50 pts of damage and so I thought "wow, that should destroy an enemy's armor in no time".

But as it turns out, even if you cast it against your foe multiple times, it does absolutely nothing to him.

So I concluded "It probably needs a longer duration" but if you give it so much as 10 seconds the total magicka cost already shoots through the roof. And that's even if you keep the magnitude low.