I've already talked about the Kansen series (the one with the nympho zombies) a bunch of times, since I posted a few pics from XX of the Dead I figured I'd share what I know on other horror themed eroge of the like.

As I mentioned, XX of the Dead is the spiritual successor to an eroge called Shokusai no Miyako by the same group, Syoku.
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Plotwise it's much like a zombie apocalypse, there's a virus that transforms it's victims into tentacle zombies, and the protagonist and his younger sister join with a group of survivors as they try to escape the city.
Personally, the body horror was a bit too squicky for me, the zombies actually look really creepy in this one and for whatever reason, they's usually transform into giant bugs. There's stuff like one of the girls transforming into a giant centipede with a human head or one where two of the girls fuse into some kind of giant slug with their heads sticking out.

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XX of the dead is more normal, the named characters who get corrupted only grow tentacles and their eyes change red with black sclera, although the generic mob zombies still look pretty grotesque. No more bugs.
My main problem was that despite having many female characters, a few of them barely got any scenes, if at all.

There's another company that did a few horror eroge called Hourglass, with two of them having a little MC. Not very much, though.

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Insai no Shima is about a group of students and a teacher visiting a deserted island, they end up getting stuck after their boat goes missing. Long story short, there are monsters in the island, the main villian beng some kinda vampire lady.
While there are routes and bad ends where some of the characters get converted, it's not a whole lot, there's only like 3 CGs with visible vampirization and most of the time characters who get vamped either get killed off shortly afterwards or simply dissappear. Still, the artwork is pretty nice, but MC-wise it's kinda dissapointing.

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Kuraki Tatari no Mori de is another one by Hourglass, this one having possession. I actually don't remember this one that well, it's been a while. Much like the previous one it's about a group of friends who travel to some resort, which turns out to be haunted.
While there's possession, it's not visibly noticable. Again, it's nice but don't bother if you're just interested in the possession

One thing I did find strange is that Insai no Shima shares a few backgrounds with the Kansen games, even their menus use the exact same layout.

Wow, thank you so much for this post. I wanted to tell you your recommendations and effort were certainly not in vain. These look so good!

There's a couple more I forgot to mention, these 2 are by Black-Cyc.

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In Mindead Blood the protagonist is an amnesiac vampire who ends up teaming up with a pair of vampire twins, rather than following the standard vampire masquerade, they decide to go out and convert the other residents of the island into vampires.
The way the games plays out is that each in-game day, you deploy the protagonist and the twins to different parts of the island. There are different chracters that inhabit these areas and by deploying the vampires to them, you can convert them. Although the victims are split into ones who can be converted by the protag or by the twins.
Each potential victim has an obedience meter which goes up everytime you deploy the appropiate vampire to their area, with them getting more devoted, and getting new sex scenes as the meter goes up. Unfortunately, once you've corrupted someone to a certain degree, a vampire hunter chick will realize they've been converted and deploy herself to that character's area.
If you do nothing, the vampire hunter will kill your servant, if you deploy the vampires to the same area, they'll intervene and try to fight the vampire hunter. I believe the phases of the moon and the amount of blood you've sucked are what determines if you can defeat her, if you're unsuccesful you'll die and get a game over. I seem to recall getting frustrated at this part.
Just a warning, the game contains scat and guro, so it's not for the faint of heart.

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I've actually never played this one and I'm not even sure if it contains MC, but the description does suggest some supernatural force is causing people to go crazy.
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I seem to recall reading a review accusing this game of being an inferior Kansen ripoff, but I don't really know anything about this.

What's really sad about Mindead Blood is that at some point a translation was in the works. Dark Translations, the group that translated Prison Battleship, started a kickstarter-esque idea where people could suggest VNs to translate, if the group found it worthwile, they'd open up a donation for that game and translate it once they recieved a certain amount of money.
Mindead Blood and 2 of the Kansen games were accepted and recieved the necessary amount of money. However, the the first game to reach the donation quota was being translated first, the other ones were put on queue and would be worked on in the order they reached quota. Unfortunately the company that made the game they were working on first sent a C&D order, and Dark Translations closed up sometime after, meaning the other games to be translated never got the chance. I wonder if all the people who donated got their money back...

Supposedly at some point JAST were interested in bringing Black-Cyc's games over here, but either they were unable to strike a deal or they were just baseless rumors. Black-Cyc also made the Yami no Koe series which I heard also contains corruption, but I've never played them.

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Here's another one I found, it's a budget game and is fairly short, but the artwork by Eroquis is pretty good.
Some weird parasitic alien begins assimilating the crew of a spaceship, the male victims turn into bizarre monstrosities while the female victims just get really horny and are then used for breeding.