Are ye talking about Act 3, Scene 2 of story mode? I use this fight for an easy Longshot daily mission (2x Advanced, 3x and 4x Expert).
River King Casino
Going All In - Expert
12th node, Bronze ONLY
Rating: 6,306 (Raw Nerv Painwheel and Primed Parasoul)
They are both Dark, so bring someone Light! I have a level 30 Bronze Headstrong Cerebella permanently staying at 1216 FS. Details:
1,216 Headstrong Cerebella
Requirements: On her skill tree, fill out the three rings of her attack damage and character ability branches. Health and Cooldown branches are at two rings, and if you want more moves, expand the Moves branch to 3 rings.
Special Moves:
Merry Go-rilla (if your spacing is right, use it, but don't gamble)
Medici Muscle (gain some armor if you need it)
Blockbusters:
Diamond Drop (make the mistake of attacking while they block? This BB will help you escape unscathed)
Ultimate Showstopper (unblockable BB3! Use this to finish the fight)
Start the match by blocking. Let them come to you. Combo, launcher, repeat. Play it safe. Practice your spacing. For instance, after launching Painwheel and doing an air combo, land and a couple dashes forward will put you in perfect Merry Go-rilla distance.