These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Game Breaker: Leveling up the Field Barrier skill to its ultimate(Field Barrier 3)makes it so that you don't have to dirty your hands on a single mook. This can be abused to gain SP for stronger skills and spells in a matter of minutes rather than 10 or 15 hours, but the tradeoff is that you don't gain any EXP.
Most Annoying Sound: Sakaguchi saw it fit to have a mechanical voice give a one-word narration to anything you do on the field or in battle. Thankfully it can be turned off.
Maro's voice is apparently designed to utterly shred the human eardrum.