Things You'll Need
Instructions
Enter The Underground area in "Pokemon Diamond." The multiplayer mode for The Underground works in local wireless mode, meaning that players will have to be in the same room or area to play.
Talk to the other player to figure out where both players are in The Underground. Navigate the tunnels to unite the two Pokemon trainers.
Face the other player once you both meet, and press the "A" button. Choose Secret Base decorations you wish to send to the player and press "A" to confirm the selections.