Games like Forest Mansion Incident
Games like Forest Mansion Incident include No, I'm not a Human, Five Nights at Freddy's: Security Breach, Outlast, Poppy Playtime, and Resident Evil Village. We matched them by the tags players give Forest Mansion Incident on Steam (Singleplayer, Horror, Multiple Endings, Choices Matter, and First-Person): closest matches first, and among equally close ones the better-known games.

No, I'm not a Human
Shared: Horror · Singleplayer · Choices Matter

Five Nights at Freddy's: Security Breach
Shared: Singleplayer · Horror · Multiple Endings

Outlast
Shared: Horror · First-Person · Singleplayer

Poppy Playtime
Shared: Singleplayer · Horror · First-Person

Resident Evil Village
Shared: Horror · Singleplayer · First-Person

Resident Evil Requiem
Shared: Horror · Singleplayer · First-Person

Resident Evil 7 Biohazard
Shared: Horror · Singleplayer · First-Person

INSIDE
Shared: Horror · Singleplayer · Atmospheric

Bendy and the Dark Revival
Shared: Singleplayer · Horror · First-Person

Choo-Choo Charles
Shared: Horror · Singleplayer · First-Person

Lethal Company
Shared: Horror · First-Person · Funny

Detroit: Become Human
Shared: Choices Matter · Multiple Endings · Singleplayer

Little Nightmares II
Shared: Horror · Singleplayer · Atmospheric

Little Nightmares
Shared: Horror · Singleplayer · Atmospheric

Bendy and the Ink Machine
Shared: Horror · Singleplayer · First-Person

Firewatch
Shared: Singleplayer · Atmospheric · First-Person

Buckshot Roulette
Shared: Horror · Singleplayer · First-Person

Outlast 2
Shared: Horror · Singleplayer · First-Person

Dishonored
Shared: First-Person · Singleplayer · Multiple Endings

The Casting of Frank Stone™
Shared: Horror · Multiple Endings · Singleplayer

Garten of Banban
Shared: Singleplayer · Horror · First-Person

Undertale
Shared: Multiple Endings · Choices Matter · Singleplayer

Layers of Fear (2016)
Shared: Horror · Singleplayer · First-Person

BioShock™ Remastered
Shared: Horror · Singleplayer · Atmospheric