So yesterday I downloaded Tetris Ultimate on the Xbox One with the hopes of playing some Tetris with my girlfriend. However, I found it incredibly difficult to figure out how to start a local multiplayer match. The menus say to add members to your party to start a Versus or Coop match, and there’s a box on the right with “friends” in it (it only lists AI players for me right now).
Even though my girlfriend was logged in, she didn’t show up on that list. I tried starting a party via Xbox with her in it, and she still didn’t show up. It turns out, any additional local player needs to press the Menu button (“start”) and then they’ll be asked to select a profile and they’ll be added to the game.
There’s no prompt for this at all that I could find, it was just by dumb luck that we finally figured out how to get her in the game. Hope this helps!
EDIT (25 January 2015): I’ve created a video now if you prefer to see how to add a second player.