If you play 2 Player mode and the second player wants to play as the same Digimon Player 1 picked, they can do so by holding down the SELECT button while selecting that same Digimon. While Calumon would usually say "Oh no..." or something like that, holding down the select button will allow Player 2 to play as an alternate coloured Digimon. This also works in vs. Computer mode for the COM player.
Also, if you want to give the 01 Digimon's partners (Agumon, Gabumon, Patamon and Gatomon) their series 1 looks instead of series 2 looks, hold down the shoulder buttons (L1, L2, R1, R2) while selecting the Digimon. This also works to give Ken his Digimon Emperor outfit when you play as Wormmon. Don't try this out on any other selectable Digimon though, it only works while selecting Agumon, Gabumon, Patamon, Gatomon or Wormmon.
Enter the password SERIUS. Or complete the game with Gabumon and Agumon.
Enter the password KIMJOY.
Enter the password LINMON.
Imperialdramon (Paladin mode):
Enter the password ROYBOY. Or complete the game with both Veemon and Wormmon in first, second, or third place.
Enter the password KENSAN.
Enter the password QRIOUS.
Play the game on any difficulty setting without losing a round (not a continue). During the fight with the last Digimon before Reapermon, BlackWarGreymon will challenge you. Beat him and Reapermon without losing a round to unlock him.
Get digivolved form:
To receive anyone's digivolved form, complete the game with them.
Get Mega form:
To receive anyone's Mega form, complete the single player game with that person. You cannot be a Mega in single player mode
THe Cheat that Mat put in is the way that I didn't get Black Wargreymon.
What you do ( and this cheat works but it isn't actually a cheat but any way) is that while you play the game, the battle may stop and say "A new challenger has entered the battle" or something like that.
Fight Black Wargreymon and you have to beat him and I think the boss as well I'm not really sure, Then you look in where your characters are then it should have on the left, top column and the second over from the left side there should be a picture of Black Wargreymon.