EX options
At the main menu, highlight the "Options" selection, then hold L + R and press A.

Hidden characters
At the character selection screen, move to the bottom row, then press Down to find Akuma/Gouki, Dan, and Devilot.

Play as Anita
At the character selection screen, highlight Donavan, then hold L + R and press A.

Play as Lin Lin
At the character selection screen, highlight Lei Lei, then hold L + R and press A.

Alternate Morrigan's form
At the character selection screen, highlight Morrigan, then hold L + R and press A to play as Morrigan in her bat form.

Full attack character
At the character selection screen, highlight any character except Dan, Devilot, Donovan, Lei Lei, and Morrigan, then hold L + R and press A