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.
Hayate: a ninja that is excessively fast, will always get a turn before your party, and can hit damage in the quadruple digits with ease, when your characters are more likely to have only 300-700 HP, and their attacks reduce your magic points.
Leaper: a harlequin-looking undead that is also extremely fast, and whose attacks have a chance of causing one-hit kills, and if they don't, they cause enough damage to likely kill you anyway, plus their attacks can drain your levels.
Most Annoying Sound: While incredibly useful, the noise that comes on when the Bishop's Magic Wall is activated becomes incredibly grating to the ears after a while. The characters' Focus unfortunately use the same noise as well.
Running into a wall (which will happen fairly frequently, either by accident or in a dark room) will cause your entire party to whine and complain. Funny the first few times, but gets quite grating afterward.