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.
Fridge Horror: To escape the mansion, you have to do elaborate puzzles that rely on items you find. At the end of the game, you see a man has gone into the mansion. He won't be able to get out because you have completed all the puzzles, so he won't be able to get the items he needs to get. Not to mention you have now let loose 3 other monsters in the Mansion...
There's also the large group of monsters you find in the basement, all of which mysteriously vanish after you've managed to get away from the two that were chasing you. And on top of that, you find cages, jail cells, and straight-up dungeons in certain areas of the mansion. Just what were those used for?
Ensemble Darkhorse: Naoki. He only shows up in one version of the game (and even then, only in a dream), but he's so popular in the fandom that he's practically become, more or less, the unofficial Sixth Ranger to the main cast.
Though it only occurs in one version, Takuro's Death by Headchomp is referenced a lot in fanwork and parodies.
Takuro is a ninja.
Nightmare Face: The faces of the monsters. Oh God, the faces of the monsters. It's especially horrible in version 6 when you have to hide in a jail cell from the monster chasing you. The game then goes completely silent and cuts to a close up of its face through the bars, at which point it grabs the bars and begins violently shaking them, and the whole time it's just staring at you with its unblinking eyes, the pupils completely dilated, lines across its face, and a large, sagging frown with big fangs. Then again...
Some people consider the blue monster's face to be adorable, goofy, or derpy rather than scary; it's even been referred to as blue Barack Obama. Or a japanese smurf. Maybe it's a suffocating Matsumoto? One member of a pair of Japanese walkthroughers (known as Borzoi Project) said that the Oni was kind of cute when they came face-to-face with it, to which his buddy responded, "Are you an idiot?"
The fact that some of them appear with hair makes it look like they're wearing hilariously bad wigs.
Paranoia Fuel: The Onis breathing. In version 6, the heavy breathing noises of the Oni are heard throughout the Dark basement. With only a lighter, you cannot see the whole screen, and the monster could pop up from any direction.
Let's just say that many of the puzzles in the game are very confusing and requires checking everything and using everything on everything else.
Version 5 in particular suffers from this due to the Cipher Puzzle. It requires knowledge of a Japanese abacus (a Soroban) and how to count using it. The English and German translator actually left a note saying they're stumped on how to translate it better for western players, and that looking it up is really the only option.