Games like 999
Games like 999 include Hollow Knight, Hollow Knight: Silksong, Defy Gravity Extended, LIMBO, and Celeste. We matched them by the tags players give 999 on Steam (Indie, Casual, Platformer, 2D, and Difficult): closest matches first, and among equally close ones the better-known games.

Hollow Knight
Shared: Platformer · Indie · Difficult

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

Defy Gravity Extended
Shared: Indie · Platformer · Puzzle Platformer

LIMBO
Shared: Indie · Platformer · Puzzle Platformer

Celeste
Shared: Indie · Difficult · Platformer

Geometry Dash
Shared: Difficult · 2D · Platformer

Cuphead
Shared: Difficult · Platformer · Indie

Braid
Shared: Indie · Puzzle Platformer · Platformer

Squishy the Suicidal Pig
Shared: Indie · Platformer · Puzzle Platformer

Nihilumbra
Shared: Indie · Platformer · Casual

Super Meat Boy
Shared: Platformer · Indie · Difficult

Toki Tori
Shared: Indie · Casual · Platformer

Rain World
Shared: Indie · Difficult · Platformer

Minimalism
Shared: Indie · Casual · Platformer

FEZ
Shared: Indie · Platformer · Casual

Nine Sols
Shared: 2D · Platformer · Difficult

Turbo Pug
Shared: Indie · Casual · 2D

Spelunky
Shared: Platformer · Indie · Difficult

BEEP
Shared: Indie · Platformer · 2D

Munin
Shared: Indie · Casual · Puzzle Platformer

Zup! F
Shared: Casual · Indie · 2D

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

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

PICO PARK
Shared: Casual · Puzzle Platformer · Platformer