The Timeline

The activity of your Partners and Rivals is displayed on this screen, and you can spectate battles and send out Nices from here. Your activity is also displayed for Partners and Rivals to see, and they can spectate and send you Nices! You can show your Status on the Timeline by tapping "Play with a Friend."

Choose "Request Tag Partner" to tell your Partners and Rivals you want to tag up.
Choose "Request Opponent" to tell them you want to battle!