Note that these cheats can't be used in championship mode: 
 
F6 - Infinite mana
F7 - Recover all 
F8 - Fall objects
F9 - Destroy objects

How to get Firzen: 
When Firen and Freeze have both less then 33% of their HP 
left and they RUN to each other a big explosion will follow 
and one of the players will gain control of the new character. 
 
How to get LouisEX: 
When Louis has got less than 33% of his HP left press: 
defend+jump+attack at the same time, then Louis will break out 
of his armor, damaging everyone near him, and transform into 
Louis Ex. Every piece of his armor counts as a heavy weapon
 
Play as Jan
Select Rudolf and if Jan pops up, grab her and press defend jump 
and attack to transform into her. You can also switch the data 
files. 
 
Play as Julian
Choose Rudolf and grab Julian when you see him. Press D, J, A to 
trasform into him! 
 
Play as Julian (alternate)
Type 'lf2.net' when open the game, then press game start. You will 
be able to select Julian. NOTE: This works in v1.9.