Games like Mantra
Games like Mantra include Outlast, Poppy Playtime, Phasmophobia, Outlast 2, and Darkwood. We matched them by the tags players give Mantra on Steam (Action, Supernatural, Psychological Horror, Survival Horror, and Survival): closest matches first, and among equally close ones the better-known games.

Outlast
Shared: Survival Horror · Psychological Horror · First-Person

Poppy Playtime
Shared: Singleplayer · Survival Horror · Psychological Horror

Phasmophobia
Shared: Psychological Horror · Supernatural · Dark

Outlast 2
Shared: Psychological Horror · Survival Horror · Singleplayer

Darkwood
Shared: Survival Horror · Action · Psychological Horror

Five Nights at Freddy's
Shared: Survival Horror · Psychological Horror · Singleplayer

Resident Evil Village
Shared: Survival Horror · Action · Singleplayer

Resident Evil 7 Biohazard
Shared: Survival Horror · Singleplayer · Action

Pacify
Shared: Psychological Horror · Survival Horror · Supernatural

The Outlast Trials
Shared: Survival Horror · Psychological Horror · Action

We Happy Few
Shared: Action · Survival · Psychological Horror

Bendy and the Dark Revival
Shared: Action · Survival Horror · Singleplayer

Five Nights at Freddy's: Sister Location
Shared: Survival Horror · Singleplayer · Survival

Slender: The Arrival
Shared: Survival Horror · Psychological Horror · First-Person

The Forest
Shared: Survival · Survival Horror · Action

Resident Evil 4
Shared: Action · Survival Horror · Singleplayer

Five Nights at Freddy's 2
Shared: Survival Horror · Psychological Horror · Singleplayer

The Beast Inside
Shared: Action · Survival Horror · Psychological Horror

Alan Wake
Shared: Action · Psychological Horror · Singleplayer

Five Nights at Freddy's 3
Shared: Survival Horror · Psychological Horror · Singleplayer

Escape the Backrooms
Shared: Psychological Horror · Survival Horror · Action

Ultimate Custom Night
Shared: Survival Horror · Singleplayer · Survival

FIVE NIGHTS AT FREDDY'S: HELP WANTED
Shared: Action · Survival Horror · Singleplayer

Dark Deception
Shared: Psychological Horror · Singleplayer · Survival Horror