UESP describes a custom spell they call Predator. Here are the details.

    * Invisibility for 2 secs on Self* Fortify Magicka 100 pts for 2 secs on Self* Fire/Frost/Shock/Health Damage x pts for 1 sec on TargetChoose the damage type according to preference; X should be chosen so that the total Magicka cost is 50 or less. As long as you keep casting the spell, your Magicka will never run out.

I'm wondering why Fortify Magicka isn't first and why the magnitude on Fortify Magicka is so high.