4P Rules are now available!
If you combine two sets of One Deck Galaxy, you can play a 4-player game! Using Tabletop Simulator, we've mocked up a birds-eye view of what that looks like at a table:
The four players sit at the edges of a square playing area (you can adjust based on your table, of course). Starbases are placed at two opposite corners of the table, and two different Adversaries at the other two corners. Each player should have one Starbase and one Adversary adjacent to them. The Discovery Zone has eight slots instead of four. Those slots are arranged so there are two cards between each pair of players.
Adjacency is key! You are "Adjacent" to the Starbase on one side of you, the Adversary on the other, the four Discovery Zone slots on either side of you, and the Homeworlds/Players to either side of you.
You're only able to interact with things that you're adjacent to. So for each corner of the table, the Locations, Encounters, Starbases/Adversaries can only be worked on by two of the four players. You'll have to carefully plan where your dice are going and communicate well in order to succeed!
For the full rules, consult the print-friendly PDF below:
Back before the Kickstarter, we streamed a 4-player game with our friends at Crit Camp Gaming, and you can see the video below! This is using a beta set of cards, and many rules have changed since. The general feel of the game is there, though!