After you have beaten the World Championship title go to the Exhibition Mode character selection screen and press square. After that press square again and you can be Jackel, Goober, Rascal, and Beastman.

To play as Jackel you first have to go to the Main Event and save any player. Then go back to Exhibition and load the player you saved by pressing square. After you highlight the player press square again and you should have Jackel in your second mystery box.

When you get knocked down rotate the d-pad and press other buttons repeatedly to get up faster.