Creepy Cute, Ugly Cute: Many characters, including Gregory himself, due largely in part to their delightfully simplistic blocky designs and ambiguously chibi appearance can come off like this.
Demonic Spiders: In the video game, residents of the hotel will chase you after you take their soul. A couple of them will be a real pain in your behind as the game goes on.
Lost Doll practically jumpscares you with how loud she screams when she sees you, and if you get caught by her she inflicts you with the Headache condition, which drains your Mental Gauge more quickly.
Hell's Chef isn't flashy, but he typically takes off about half your Mental Gauge whenever he catches you. Cactus Gunman likewise deals a lot of damage, but he isn't nearly as aggressive as Hell's Chef is.
Clock Master and My Son don't actually hurt you, but use their time powers to flash you forward in time, possibly messing you up on time-sensitive events.
And then of course, as the game goes on and you gain more enemies, it's practically impossible to avoid getting spotted in the halls without very thorough planning. Catherine, Lost Doll, Mummy Dog and Mummy Papa, Cactus Gunman and his sister, Hell's Chef, and Clock Master and My Son will all be gunning for you at the end of the game, so it's not uncommon to be subjected to one Horror Show and then immediately get caught by someone else directly afterwards.
People love Judgment Boy just as much, if not more.
Kinko and Inko have seem to have a small following as well.
Dr. Fritz, too.
Jerkass Woobie: Gregory is a Dirty Old Man hell-bent on keeping unfortunate guests inside of his Hell Hotel, and doesn't seem to feel any remorse about it. He's also been heavily abused by his mother, who seems to be the one thing keeping him at Gregory House, and has recurring nightmares as a result. It's hard not to feel at least a little bad for him, with all that he puts up with.
Catherine often gives off some creepy undertones when she's collecting blood with her giant syringe; even so, it's hard to not feel bad for her when she mistakenly believes Hell's Chef is sending her love letters, only for him to yell at her and hit her.
Clock Master is pretty arrogant and somewhat rude, but it is pretty sad to see how upset he is that his abilities to control time are lessening as he grows older. It gets worse in the second series when you see it's even driven him to drinking.
Moral Event Horizon: Gregory for torturing and rendering Neko Zombie as he is now, while keeping him imprisoned in the hellish hotel. And Gregory Mama, for capturing and consuming lost souls all for revitalizing her "beautiful" self.
We also see his mother and James and they don't look so good either.
TV Fish is generally the most benign resident of Gregory House in that it doesn't outright try to kill or harm anyone. But it also projects memories of those it comes in contact with, particularly painful memories...
Neko Zombie may not be especially scary at first glance, but what was done to him is pretty horrific: someone (heavily implied to be Gregory) sewed his mouth, ears, and eyes shut and chained him up in a room in Gregory House, leaving him half-starved most of the time. It's even worse seeing as he's one of the few truly benevolent residents of the hotel.
Hell's Roulette is Mario Party on crack! With a host who really seems a bit too excited for others to play his game, without any of the skill and add in the fact that you will likely be getting hurt is there any wonder why Gregory gets scared when he has to play it?
The warp Gregory goes through in the Last Train. First he sees a version of his mother asking him to open his eyes before eating him. Then he thinks it's over until he sees a bunch of lost souls in the train. Before he can fathom why they are there, he sees another him who gives him some keys. After the warp ends for good, Gregory wonders if he has to return to Gregory House as the episode ends.
While epic at the same time, the boss fight with Gregory Mama in the game is this as she at first laughs evilly as she pelts the guest with fireballs only to become more angry as the door breaks down.
No Problem with Licensed Games: Yes, The Gregory Horror Show actually got a video game, and its considered one of the best licensed games ever made to those who played it. Sadly it never left the United Kingdom or Japan.
One-Scene Wonder: A good handful of the characters in the series only pop up in one short for the entire run.
That One Boss: The Clock Master and My Son in the game. By the time they've shown up, the player has already stolen the souls of 11 guests. 8 of those guests are hostile and will attack the player if they see them. Clock Master's ability means that he can appear in front or behind the player as he chases him/her. Because of this, the Clock Master can change the direction of the chase, and is very likely to make the player run into another hostile guest as they're fleeing him. Even heading to the mostly-abandoned basement means risking an encounter with Roulette Boy or Lost Doll in the dark. And just to wrap it all up, the player has to quickly find My Son in order to get their soul before Clock Master recovers.
What Do You Mean, It's Not for Kids?: Quite honestly, the show seems innocent enough; sure, it has "horror" in the title, but the fact that it has an anthropomorphic mouse as the main character means it could easily be mistaken for something along the lines of Goosebumps or Courage the Cowardly Dog. However, once you get to Catherine in episode 6, a snake nurse who makes orgasmic moans as she draws your blood through a syringe, things start to get a little rocky. Later on when the "splitting headaches" of Mummy Dog and Mummy Papa show up, there's plenty of Nightmare Fuel to show this is far from a show for children. Believe it or not, it was created by the same person who created Pecola. Thankfully, Netflix re-categorized the series from "Kids and Family" to "Anime Horror" after complaints.
Neko Zombie is this in his entirety. Prior to being the undead half-cat creature he is now, he was an ordinary house cat with a loving owner and lived a happy life. Then Gregory appeared, killed his owner, and took him for himself, turning him from a happy cat to the tortured Neko Zombie. It makes him all the more impressive that he's actually benevolent after all that happened to him, as well as that he's chained to the corner of a room that looks like a prison cell.
The Second Guest is a bit of this as well. She had just left from a wedding when she found Gregory House, a wedding between her best friend and her ex-boyfriend. Her ex had broken up with her after she said she wanted to work on her career first before she got married, and apparently she never got over it. You can see her slowly beginning to break down because of this as the series goes on.
Haniwa Salaryman and Sleepy Sheep as well.
Even Catherine thinks this of Haniwa in The Bloody Karte.