See the theory above.
Depends are we talking about our magic users because yours are probably a bit better at it, or shard to shard combat?
In terms of magic systems mine requires you to not itch yourself(yes it's super frustrating as is telling you what is explicate) then apply that to things that frustrate people, so nothing terribly useful, streaks on glass, socks and saddles and the like. Best case scenario imperfections in your opponents weapon, or making them sneeze.