Cheats
Note that these cheats can't be used in championship mode:

F6 - Infinite mana
F7 - Recover all
F8 - Fall objects
F9 - Destroy objects

Unlock All Fighters
Unverified. Input lf2.net in the main menu. You have to type the normal fullstop not the one on the number/calculator pad.

Hack - All Characters
Locate the data.txt file in the game directory. Open it with Notepad and search for the string id: 11 type: 0 file: data\davis.dat and append the following lines:

id: 12 type: 0 file: data\louisEX.dat
id: 13 type: 0 file: data\knight.dat
id: 14 type: 0 file: data\bandit.dat
id: 15 type: 0 file: data\hunter.dat
id: 16 type: 0 file: data\mark.dat
id: 17 type: 0 file: data\jack.dat
id: 18 type: 0 file: data\sorcerer.dat
id: 19 type: 0 file: data\monk.dat
id: 20 type: 0 file: data\jan.dat
id: 21 type: 0 file: data\firzen.dat
id: 22 type: 0 file: data\justin.dat
id: 23 type: 0 file: data\bat.dat
id: 24 type: 0 file: data\julian.dat

Save the file and reboot the game to see the force added cast. (Unverified)