TLDR Version: Browse local files and launch the server. Set your custom server address to "localhost". Launch a 2nd version of the game from the local files so you have 2 "players" then go to multiplayer, create a join and have the 2nd client join the server and hit ready ready and you're in.

There's some glitches but you can get some of the achieve-o's ~ this way.

Scenic Route:

Step the First!

You will need to browse to your local files which can be done from the steam app as shown.


In there, you will find an executable called "Jubilane_server", launch it by double clicking.


You will see this screen. Click "Begin Hosting" and it will disappear and the server should be started.


Now you will have to go set the server address in the game so launch your game twice. You can easily do this by launching the Jubilane executable in the local files twice. They will share the same settings so you only have to do this once.

Go into the options menu and click custom server at the top right then type localhost into the field below.


Now go back and hit Online to join the lobby. It should connect you straight away. Create a Room.


Then have your other client join that same room. It will appear under the send button.


Once you have 2 people in the lobby you will have the option to ready up. Do this for both clients.


Once you have done that, a new button will appear on the client who created the room that says, "Begin Play".


And that's it! You did it! Now you can play multiplayer! :)