I saw many people asking for others to help them earn the traitor achievement. So I tried to find a way to do it on my own.

You can earn the traitor achievement solo by launching two instances of the game.

Tips

• If you expect that your computer can't handle running the game twice, you can turn the graphics down beforehand.
  
• A smaller resolution and windowed mode can make it easier to switch between clients.

Note: This guide probably has more steps than necessary, but I already earned the achievement and was not able to test in more detail.

1. When launching the game, Steam should give you the option to launch the game in multiplayer.
   
   
2. This should give you the option to select multiplayer in the game menu.
   
   
   
3. Select "Direct connection"
   
   
   
4. Select "Start Server"
   
   Note: If an error pops up, you maybe have to change the last number(7777) to something higher like 7778. The reason for this is that this port is probably already in use by another server(like e.g. Terraria, which uses the same port by default).

Now choose your save and everything should work the same as in singleplayer.

1. Open the local files of the game
   
   
   
2. You should see 2 folders. Choose MP for multiplayer
   
   
   
3. Here you can launch the .exe file. This should start up a second game.
   
   Note: If you have trouble navigating you can put the game in windowed mode or use alt+tab to switch between windows.
   
   
4. When the game has started first go to characters and make or pick another character than the one used in the other running game.
   
   
5. Go back to the main menu en go to "multiplayer" > "Direct connection" > "Join Server", Note: if you changed the port last time you should change it here to the same number.

After that you should get into the same game as the other character.
If you don't and the game has put you back in the main menu then something went wrong with the connection to the server.

The achievement might not show until you return to singleplayer!

To get the achievement you need to kill another player. So with your main account (the one you launched first with Steam) you should kill the other player.

Tip: Try to do this with a sword or something else with enough damage.
Note: for me a wand didn't deal any damage so it's possible that ranged weapons don't work.

I didn't receive the Steam achievement until I got back in my game via singleplayer.

1. Close both games.
   
2. Start the game again in singleplayer via Steam.
   
3. Pick the main character (the killer) and start your save.

Now you should have received it.