Unlock Judgment: the letters in "Judgment" are hidden in chests in level 6-1. Find them all to unlock the character.
To unlock Characters, do the following tasks:
Anji Mito: finish Stage 3-2 With Slayer
Axel Low: finish Stage 3-1 with Chipp Zanuff
Baiken: finish Stage 2-1 with Millia Rage
Bridget: finish Stage 2-1 with Ky Kiske
Chipp Zanuff: finish Stage 2-1 with Sol BadGuy
Dizzy: finish Stage 2-1 with May
Eddie: finish Stage 2-1 with I-NO
Faust: finish Stage 4-2 with Sol BadGuy
Jam: finish Stage 3-2 with Potemkin
Johnny: finish Stage 2-2 with Dizzy
Potemkin: finish Stage 3-2 with Bridget
Slayer: finish stage 2-2 with Millia Rage
Testament: finish Stage 4-2 With May
Venom: finish Stage 3-1 with Eddie
Zappa: finish Stage 2-2 with I-NO