Is Owlboy Co-op or Multiplayer? Single-Player Only
Owlboy's Steam features list Single-player only, so there is no local split screen, online co-op, or crossplay.
Is Owlboy Co-op or Multiplayer? Single-Player Only
No. According to the game's Steam store page, Owlboy is a single-player game only. Its listed Steam features include Single-player but nothing for co-op, local multiplayer, or online play, and the official store description never mentions a multiplayer mode. No co-op, split-screen, or crossplay option appears in the official materials, so on the documented evidence you should expect to play it alone.
What the store listings say
The Steam feature list for Owlboy names Single-player alongside Steam Achievements, Full controller support, Steam Trading Cards, Steam Cloud, Steam Leaderboards, Remote Play on TV, and Family Sharing. That list does not include any shared-screen or online co-op feature. The official description frames the experience as a solo story: you fly, explore, and carry Otus's friends with you as gunners.
Family Sharing is not co-op
Family Sharing appears among the Steam features, and it is easy to misread. It allows different accounts to access a shared library; it does not let two people play Owlboy together at the same time. Nothing in the official facts describes simultaneous play of any kind.
A solo adventure by design
The game's core loop is built around one player controlling Otus in flight and platforming while carrying a gunner companion. The official store text describes picking up friends and bringing them along as gunners to fight for you, each with unique abilities and stories. That partner system is part of the single-player campaign, not a second-player mode.
Other platforms
The Nintendo listing lists the player count as one, single system only, which points the same way. The GOG page also lists Single-player among the game features. Taken together, the official listings present Owlboy as a solo experience on every platform where details are given.
Bottom line
If you are looking for a game to play with a friend, Owlboy does not offer that according to its official store listings. It is a single-player action adventure. For background on the game and its genre, Rock Paper Shotgun's Owlboy page collects related coverage, though anything beyond the official facts above should be treated as outside documentation.
Related Guides
Owlboy Auto-Aim: How to Turn It On or Off
Where to find the Owlboy auto-aim setting, what it changes about aiming with controllers, and whether you can still aim manually.
Owlboy Beginner Guide: Flying, Attack, and Exploration Basics
A starting-point guide for new Owlboy players covering the core loop: flying as Otus, carrying and using gunners, the spin attack, throwing pickups, and exploring the sky world.
Owlboy Core Mechanics Explained: Flight, Gunners, Spin Attack, and Throw
Explains Owlboy's fundamental systems: constant flight, carrying friends as gunners, the spin attack and shooting, and throwing pickups.
How to Use Super Dash in Owlboy
How the Super Dash works in Owlboy, which button to hold, and how it improves on spamming the roll button for faster movement.