Hold down the designated button while selecting Arcade Mode. If done correctly you should be fighting the specified opponents.
To unlock Kliff and Justice do the following
Through survival mode,you can unlock EX and SP characters.
After LV 500 youj will start fighting Gold characters instead of the EX ones in the order they appeared in EX forms.
After unlocking the SP forms,Press start at the unlocked character then press right at the Directional stick.