Games like Girl with gun
Games like Girl with gun include Buckshot Roulette, No, I'm not a Human, Outlast, MiSide, and Poppy Playtime. We matched them by the tags players give Girl with gun on Steam (Psychological Horror, Horror, First-Person, Singleplayer, and Dark): closest matches first, and among equally close ones the better-known games.

Buckshot Roulette
Shared: Horror · Dark · First-Person

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

Outlast
Shared: Horror · First-Person · Psychological Horror

MiSide
Shared: Psychological Horror · Horror · First-Person

Poppy Playtime
Shared: Horror · Singleplayer · First-Person

CloverPit
Shared: Psychological Horror · First-Person · Horror

Mouthwashing
Shared: Psychological Horror · Horror · Atmospheric

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

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

Outlast 2
Shared: Psychological Horror · Horror · First-Person

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

SOMA
Shared: Psychological Horror · Horror · Atmospheric

Visage
Shared: Psychological Horror · Horror · Dark

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

Phasmophobia
Shared: Horror · Psychological Horror · First-Person

Garten of Banban 2
Shared: Horror · First-Person · Singleplayer

Little Nightmares
Shared: Horror · Singleplayer · Atmospheric

Garten of Banban 3
Shared: Horror · Psychological Horror · First-Person

Little Nightmares II
Shared: Horror · Singleplayer · Psychological Horror

Escape the Backrooms
Shared: Horror · Psychological Horror · First-Person

Amnesia: The Dark Descent
Shared: Horror · Psychological Horror · First-Person

Five Nights at Freddy's 4
Shared: Horror · First-Person · Singleplayer

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

From The Darkness
Shared: Psychological Horror · Horror · First-Person