Background Select:
At the character select screen, highlight Sonya and press Up+Start. After you select your character, you can then toggle through the backgrounds to choose the one you want.

Play as Chameleon:
To play as Chameleon choose any male Ninja at the character select screen. Press and hold Left, High Punch, Low Punch, Run and Block until the match starts.

MK Classic Fighters:
In the player select, highlight any one of these characters; Kung Lao, Kano, Raiden or Jax and press Select for play with classic fighters.

Thanks to Revolution readers Jim Hirabayashi and Nicolas Mendez!