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.
Good Bad Bugs: Several; one of the more famous ones is the saw weapon. It's supposed to inflict instant death on a target whose defense is lower than the user's strength, but instead kills enemies whose defense is higher than your strength. Meaning it works on the final boss. Meaning you can kill God with a chainsaw.
Also worth noting is that the insanely powerful Glass Sword was supposed to break after only one use. Due to an error in translation, it gets a full 50 uses in the NA version.
Character stats appear to be capped at 99, but can actually be increased up to 255. (If you increase them any more, they wrap around back to 0.) The hit point maximum can also be increased beyond its apparent cap of 999.