The only thing I've seen is what I assume is a bug, but I'll have enemy units on my NK, they'll take a bar.
When the explosion happens, the enemy units might not get knocked back at all, and sometimes won't lose HP either.
The units appear to get killed for a moment, and then they warp back to my NK where they were before the explosion.
This happens on average 1/10 games where I lose a bar which makes that a fairly common problem.

I have also seen one energy hack in my entire time playing, and it was about a month ago and someone played 9 units in like 4 seconds.