The following information is out of date, please find the latest info in the following video and FAQ post:

Due to complications with development we are no longer developing true multiplayer, instead we're taking a splitscreen approach due to issues with physics engines.
Dev Vlog:
https://www.youtube.com/watch?v=OO1Q20fUUBs
FAQ Post:
https://steamcommunity.com/app/1106840/discussions/0/3203748171375176286/

…We've got some bad news unfortunately.
Please watch through, where we talk features, game development and delays.
https://youtu.be/6-72888KJEQ