I figured out a way to get an infinite combo with Mr. Game and Watch. This is extremely useful if you want to get the secret trophies that require a certain number of combos in training mode.
First, go to training and select Mr. Game and Watch. for the COM, select any character (I used Fox). Then select Shadow Moses Island.
Once it starts, make sure to keep the COM on stationary. Also make sure to turn on the Extra Help display on the right, because sometimes you'll think you're performing a combo when you actually aren't. Jump over and push the COM into the wall (either side works). Then position yourself in front of the COM and hold down the basic attack button (A for the GC controller). If you're correctly positioned, the COM will be hit, but won't be able to move back due to the wall. If you're too close or too far, the wall will be hurt by your blows (it will break and you'll be able to only get up to 25 for your combo) or the COM will be hit infrequently enough for it to not count as a combo . If one of these happens, reposition yourself. However, if all goes well, continue to hold down the attack button and Game & Watch will continue to hit. This can honestly go on forever, but the game will stop counting at 999. If you use this and get to 999 (which I did) then you can get the challenge trophies easy
What do you think? If you have any problems, post them here!