So the description should be:
This issue of Combat King will teach the reader how to break opponent's concentration with each offensive magic type ability. Destroys mana of the attacked enemy unit equal to X% of the reader's maximum mana and enemies with less than X% mana that are hit by the reader's spells have a(n) X% chance to be stunned for 2 seconds.
I don't think that it would be a good high tier combat king though. Medium tier would be better.