To play as any of the Bonus characters, enter "lf2.net" during the loading screen or while you're on the character selection screen. This cheat also unlocks a new difficulty: "CRAZY!"
2) Fusion
3) Transform from Louis to LouisEX
There's also a way to play as Firzen without the cheat. If Firen and Freeze are on the same team and they both have less than 1/3 of their hp, then if they run into the other, Firzen will appears with a giant explosion. The player who is running to the left will control Firzen while the other player will disappear. To split back into Freeze and Firen, press DJA
You can also use Louis to transform into LouisEX when you have under 1/3 of your total hitpoints. Press the keycombination [Defend] + [Jump] + [Attack] and Louis will throw his armour away and change into LouisEX. The armour lies around as heavy weapons.
4) Pause Game without Pause-Logo (only for versions prior to v2.0)
If you press F10 during gameplay the game will pause without showing the Pause-Logo. Very practical for Screenshots. The only bad about this: If you press F10 during walking and end pause you walk without pressing a key - just start an attack or run and you'll go to "normal control" again...