Peter Shorts' big birthday update is almost ready! You can opt-into the public_beta branch to try it out!
Enter the door titled PLAY ONLINE (to the left of the title) to create/join a lobby.
All game modes are supported, including VS mode, Story mode, and all the side-games. All modes and characters will be temporarily unlocked when playing online.
Please send any bug reports to the megathread on the Steam Community forum, or in the comments on this post.
Full patch notes will be available once the update is pushed to the main branch.