Games like Mystery Castle
Games like Mystery Castle include Pikuniku, LIMBO, BEEP, There Is No Game: Wrong Dimension, and Out There Somewhere. We matched them by the tags players give Mystery Castle on Steam (Indie, Action, Adventure, Puzzle, and 2D): closest matches first, and among equally close ones the better-known games.

Pikuniku
Shared: Indie · Adventure · Puzzle

LIMBO
Shared: Indie · Puzzle · Adventure

BEEP
Shared: Indie · Adventure · 2D

There Is No Game: Wrong Dimension
Shared: Indie · Puzzle · Adventure

Out There Somewhere
Shared: Indie · Puzzle · Adventure

BADLAND: Game of the Year Edition
Shared: Indie · Adventure · Action

Skul: The Hero Slayer
Shared: Indie · Action · 2D

Human Fall Flat
Shared: Puzzle · Adventure · Action

Gunpoint
Shared: Indie · Puzzle · 2D

Dust: An Elysian Tail
Shared: Action · Indie · Adventure

CARRION
Shared: Action · Indie · 2D

Deliver Us The Moon
Shared: Indie · Adventure · Action

ICEY
Shared: Action · Indie · Adventure

UFO 50
Shared: Indie · Action · 2D

SANABI
Shared: Action · Adventure · Indie

Mark of the Ninja
Shared: Indie · Action · 2D

Dungeon Munchies
Shared: Indie · Action · Adventure

Rocketbirds: Hardboiled Chicken
Shared: Indie · Action · Adventure

Deadlight
Shared: Action · Indie · Adventure

Seen
Shared: Indie · Adventure · Puzzle

Hollow Knight: Silksong
Shared: Indie · 2D · Adventure

Terraria
Shared: 2D · Adventure · Indie

Broforce
Shared: Action · 2D · Indie

Zombotron
Shared: Action · Indie · Adventure