This is ridiculous trying to get a guest user added to play with a group of friends online. It took almost 45 minutes until we figured out the correct sequence to add a guest to play horde on XBOX live.

Controller 2
Click Y to add Guest
Controller 1
Click A to accept
Controller 2
Click Y again to add Guest
Controller 2
Select Guest Xbox Live user.

Done.

FYI At no point should you select to sign in a secondary account local on the xbox. This kept throwing us off. What as the point of having to select twice.

ZeroRecon