Play as Chase:
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Defeat Mala Mala Jong in the last level of Adventure mode
to unlock Chase.

Play as Jack:
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Get at least halfway through the game to fight the Jack
Spicer Robot. Defeat it to unlock Jack.

Alternate costumes:
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To unlock new costumes, level up the rank from Grass Hopper
in Training mode to Wudai. For some ranks it will unlock new
costumes:

Monk costume
Showdown costume
Robot costume
Street costume