Kayle Ult.

Kayle is a low mana cost champ, so something like this wouldn't destroy her in the least. Would only make kayle players consider their mana more which would be a little nice.

It should have both a mana cost and increased cooldown.

You can disable the target of her ultimate, and she has to sacrifice a hotkey slot to self-cast reliably. Disables alone are making the ability fine. Adding a mana cost would break her.

Dude... that's all I have to say