Games like Mystic Explorer
Games like Mystic Explorer include Vampire Survivors, Megabonk, Enter the Gungeon, I Am Legion: Stand Survivors, and 20 Minutes Till Dawn. We matched them by the tags players give Mystic Explorer on Steam (Bullet Hell, Loot, 2D, Casual, and Pixel Graphics): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Bullet Hell · Pixel Graphics · 2D

Megabonk
Shared: Bullet Hell · Roguelike · Loot

Enter the Gungeon
Shared: Bullet Hell · Pixel Graphics · Roguelike

I Am Legion: Stand Survivors
Shared: Bullet Hell · Loot · Shoot 'Em Up

20 Minutes Till Dawn
Shared: Bullet Hell · Shoot 'Em Up · Pixel Graphics

Death Must Die
Shared: Bullet Hell · Pixel Graphics · 2D

BALL x PIT
Shared: Bullet Hell · Roguelike · Pixel Graphics

Balatro
Shared: Roguelike · Pixel Graphics · Casual

Noobs Want to Live
Shared: Bullet Hell · Pixel Graphics · Roguelike

Realm of the Mad God Exalt
Shared: Bullet Hell · Pixel Graphics · Roguelike

Boneraiser Minions
Shared: Bullet Hell · 2D · Pixel Graphics

Necrosmith
Shared: Bullet Hell · 2D · Roguelike

Halls of Torment
Shared: Bullet Hell · Pixel Graphics · Roguelike

Neon Abyss
Shared: Loot · Roguelike · Pixel Graphics

Asgard's Fall — Viking Survivors
Shared: Bullet Hell · Casual · Pixel Graphics

Rocket Rats
Shared: Bullet Hell · Pixel Graphics · Casual

Star of Providence
Shared: Bullet Hell · Pixel Graphics · Shoot 'Em Up

Dead Cells
Shared: Roguelike · 2D · Pixel Graphics

Skul: The Hero Slayer
Shared: Pixel Graphics · 2D · Roguelike

The Binding of Isaac: Rebirth
Shared: Roguelike · Pixel Graphics · Indie

Nuclear Throne
Shared: Bullet Hell · Pixel Graphics · Roguelike

Apocalypse Party
Shared: Casual · Bullet Hell · Roguelike

Brotato
Shared: Bullet Hell · Roguelike · Singleplayer

Planes, Bullets and Vodka
Shared: Casual · Bullet Hell · 2D