Change characters before fight:
Enter it in at the versus screen after you select your characters, and hold it until the match begins

Assist 1 - Swaps first and second characters
Assist 2 - Swaps first and third characters
Assist 1 + Assist 2 - Swaps second and third characters

Level Clock:
Whenever you play either clock tower stage, the clock in the background will be set to real-world time, as long your dreamcast's internal clock is.

Hidden Characters:
For Less Points To get the hidden characters at lower prices, keep on entering and exiting the shop. Eventually, the hidden characters will cost less.

Choose A Character Multiple Times On A Single Team:
Unlock all the costumes and hidden characters to be able to choose the same character mutiple times on the same team.

Attack Opponent After Winning a Match:
After you win a match and your character does his/her victory pose, press Start. You'll be able to attack your fallen opponent while he/she is down.

Free Bonus Credits:
Set the game in Training Mode and let it sit--every minute you let the game sit will earn you more points used for unlocking characters and costumes. You can earn up to 9,999 points at a time doing this.