Games like Wildcat Gun Machine
Games like Wildcat Gun Machine include Enter the Gungeon, Exit the Gungeon, Vampire Survivors, Bit Blaster XL, and Cuphead. We matched them by the tags players give Wildcat Gun Machine on Steam (Bullet Hell, Action, Twin Stick Shooter, Difficult, and 2D): closest matches first, and among equally close ones the better-known games.

Enter the Gungeon
Shared: Bullet Hell · Difficult · Dungeon Crawler

Exit the Gungeon
Shared: Action · Bullet Hell · Arcade

Vampire Survivors
Shared: Bullet Hell · 2D · Singleplayer

Bit Blaster XL
Shared: Bullet Hell · Difficult · Action

Cuphead
Shared: Difficult · 2D · Bullet Hell

Geometry Dash
Shared: Difficult · 2D · Singleplayer

Dead Estate
Shared: Twin Stick Shooter · Bullet Hell · Difficult

LUFTRAUSERS
Shared: Bullet Hell · Action · 2D

Touhou Koumakyou: New Classic - the Embodiment of Scarlet Devil
Shared: Bullet Hell · Difficult · Action

Windowkill
Shared: Action · Bullet Hell · Twin Stick Shooter

Nex Machina
Shared: Bullet Hell · Twin Stick Shooter · Action

A Dance of Fire and Ice
Shared: Difficult · Singleplayer · 2D

Hollow Knight: Silksong
Shared: Difficult · 2D · Singleplayer

Just Shapes & Beats
Shared: Bullet Hell · Difficult · Action

RUINER
Shared: Action · Twin Stick Shooter · Difficult

BALL x PIT
Shared: Action · Bullet Hell · Arcade

UBERMOSH
Shared: Action · Bullet Hell · Twin Stick Shooter

Ikaruga
Shared: Bullet Hell · Action · Difficult

SYNTHETIK: Legion Rising
Shared: Action · Difficult · Twin Stick Shooter

Touhou Tenkuushou ~ Hidden Star in Four Seasons.
Shared: Bullet Hell · Difficult · Singleplayer

Nuclear Throne
Shared: Bullet Hell · Difficult · Action

Star of Providence
Shared: Bullet Hell · Action · Difficult

Brigador: Up-Armored Edition
Shared: Action · Twin Stick Shooter · Difficult

Assault Android Cactus+
Shared: Bullet Hell · Twin Stick Shooter · Difficult