Enter this code while playing to drop your weapon. The primary uses of this is that sometimes the CPU enemy will do the same.
Also, winning a match without a weapon equipped (it can also be knocked from a character's hands by powerful moves) will result in a different victory animation.
At the main screen, hold down Start, highlight Options, and press A to enter the Options menu. Highlight Exit and press A + B + C + D simultaneously, and release Start.