Games like Ontotis
Games like Ontotis include Firewatch, What Remains of Edith Finch, Mouthwashing, SOMA, and SILENT HILL 2. We matched them by the tags players give Ontotis on Steam (Psychological Horror, Atmospheric, Mystery, Story Rich, and Action): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Atmospheric · Story Rich · Adventure

What Remains of Edith Finch
Shared: Atmospheric · Story Rich · Mystery

Mouthwashing
Shared: Psychological Horror · Atmospheric · Story Rich

SOMA
Shared: Psychological Horror · Atmospheric · Story Rich

SILENT HILL 2
Shared: Psychological Horror · Story Rich · Atmospheric

Outer Wilds
Shared: Mystery · Story Rich · Atmospheric

No, I'm not a Human
Shared: Psychological Horror · Atmospheric · Horror

Amnesia: A Machine For Pigs
Shared: Atmospheric · Story Rich · Psychological Horror

Alan Wake
Shared: Action · Story Rich · Atmospheric

Layers of Fear (2016)
Shared: Psychological Horror · Atmospheric · Horror

Sally Face - Episode One
Shared: Psychological Horror · Story Rich · Mystery

SILENT HILL f
Shared: Psychological Horror · Story Rich · Horror

MiSide
Shared: Psychological Horror · Story Rich · Atmospheric

Darkwood
Shared: Psychological Horror · Adventure · Horror

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Story Rich · Psychological

Poppy Playtime
Shared: Psychological Horror · Horror · Mystery

Raging Loop
Shared: Mystery · Psychological Horror · Adventure

Outlast
Shared: Atmospheric · Psychological Horror · Horror

Little Nightmares II
Shared: Atmospheric · Adventure · Psychological Horror

The Park®
Shared: Psychological Horror · Atmospheric · Horror

Still Wakes the Deep
Shared: Psychological Horror · Horror · Story Rich

Little Nightmares
Shared: Atmospheric · Adventure · Horror

Fears to Fathom - Ironbark Lookout
Shared: Psychological Horror · Atmospheric · Horror

[Chillas Art] The Convenience Store
Shared: Psychological Horror · Atmospheric · Horror