There are two ways to join other player's games in D2:R:
Method 1 - Joining from friends list
1) If you are in-game: Hit enter and open your friends list by clicking this icon:
- You can also browse your friends list from the lobby. Click on the same icon on the left side.
2) Click on " Add Friend " at the bottom.
3) Add the other person to your friend list by entering their battle tag. (example#1234)
4) You can now join their game from any region by right clicking on their name and selecting " Join Game ".
Method 2 - Changing your region
1) Close the game and open up the battle.net client.
2) Where you press " Play " you will see a small globe icon:
3) After clicking on this icon, you will get the option to change region (Americas -> Europe -> Asia)
4) Select the region and launch the game.
Note: If you are on a different region than the person who's game you are trying to join, you will receive this error: