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.
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.
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.
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.
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.