One of the trophies in the Challanges is the Ouendan trophy. In order to get this trophy, you have to get 400 combined max combos with all characters in training.
That will take quite a while. But the Brawl strategy guide shows you an easier way that will take you 2 minutes tops.
To get 400 combined max combos with all characters in Training for the Ouendan trophy, select Kirby and head to the Temple(Melee) stage. Go to the Pause menu and "CPU" to "Control" and change "HELP" to "ON". Push your training partner to the side of the platform, just to the left of their starting position. Move to their right side so they are pinned against the platform, and hold the Attack button to initiate Kirby's multihit standard attack. Because they are pinned against the platform, they do not move and the number of hits continues to mount. The consecutive hits tally on the left is the max combo total as well. When it hits 400, you can exit out of Training to receive the Ouendan trophy.