Games like The Dark Realm
Games like The Dark Realm include Vampire Survivors, Enter the Gungeon, The Binding of Isaac: Rebirth, Megabonk, and Nuclear Throne. We matched them by the tags players give The Dark Realm on Steam (Action Roguelike, Bullet Hell, Roguelite, Difficult, and Roguelike): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Action Roguelike · Bullet Hell · Roguelite

Enter the Gungeon
Shared: Action Roguelike · Bullet Hell · Roguelike

The Binding of Isaac: Rebirth
Shared: Action Roguelike · Roguelike · Difficult

Megabonk
Shared: Action Roguelike · Roguelite · Roguelike

Nuclear Throne
Shared: Action Roguelike · Roguelike · Bullet Hell

Skul: The Hero Slayer
Shared: Action Roguelike · Roguelike · Pixel Graphics

Halls of Torment
Shared: Action Roguelike · Bullet Hell · Roguelite

Hades
Shared: Action Roguelike · Roguelite · Roguelike

Death Must Die
Shared: Action Roguelike · Bullet Hell · Roguelite

Dungreed
Shared: Action Roguelike · Roguelite · Roguelike

Tiny Rogues
Shared: Action Roguelike · Bullet Hell · Difficult

BALL x PIT
Shared: Roguelite · Bullet Hell · Action Roguelike

Brotato
Shared: Bullet Hell · Action Roguelike · Roguelike

Atomicrops
Shared: Bullet Hell · Roguelike · Action Roguelike

Sephiria
Shared: Action Roguelike · Roguelite · Roguelike

Star of Providence
Shared: Bullet Hell · Action Roguelike · Roguelite

20 Minutes Till Dawn
Shared: Action Roguelike · Bullet Hell · Roguelite

Risk of Rain 2
Shared: Action Roguelike · Roguelite · Roguelike

Dead Cells
Shared: Action Roguelike · Roguelike · Roguelite

The Binding of Isaac
Shared: Action Roguelike · Roguelike · Difficult

Noobs Want to Live
Shared: Bullet Hell · Roguelike · Action Roguelike

Risk of Rain (2013)
Shared: Action Roguelike · Roguelike · Pixel Graphics

Soulstone Survivors
Shared: Action Roguelike · Roguelite · Bullet Hell

Noita
Shared: Roguelike · Difficult · Pixel Graphics