Mana Drain + Defend, Best way to do it?

[Fenrik]

I have a Hero Skill that is Defend. However, I'd like to make it cost mana per second. What's the best way to do this? I know I could make a really complicated trigger involving immolation and checking the levels of both abilities.. blah blah. I hope there is a better way though.

The mana drained per second decreases as the level of the ability increases, preferably.

 

[Red Orca]

Im using a mana drain system via triggers. . . I got it from Vegeta_SS's transform map, go to the spells section and search transform.