I've never noticed it to have a range limit as plenty of longshots have drained energy. It and Keening do seem to be randomly resisted at times, though, regardless of the range.

Interesting... The UESP on Keening says that it delivers "Keening's Sting" on a hit which can be resisted with magic resistance. Nothing on Black Bow though. Maybe it tries to absorb magicka from an enemy with no magicka...?

That's what I was thinking. I've had Keening resisted by dragons, who have 25% fire & frost resistance.

It should be general magic resistance not fire or frost based on a description. I don't know if there are even enemies immune to magic or having some magic resistance 

I guess I should test this out on the boss from the Only Cure quest.

Does he have magic resistance? I think Ebony Warrior will have it 

Orchendor has complete absorbtion resistance according to the wiki.

UESP doesn't mention anything like that (Link). I didn't notice anything like that in my game too.

Actually it's just that I played the automation earlier and this build was just too cool to delay when I thought of it. Playtesting it was quite fun.

How is this still in the Bloodworks? This is a gem.