Samurai Shodown

Fight as Amakusa:
Quickly press A, Y, X, B at the Takara logo screen. Hold L + R during character selection in versus mode or countdown mode to transform into Amakusa.

Alternate costumes:
Highlight any character and press Select, Y, or X while choosing them. Note: This cannot be done in Count Down mode.
Information in this section was contributed by Louie.

Fight as Wan Fu's Brother:
Highlight Wan Fu and press Select, Y, or X while selecting him.
Information in this section was contributed by Louie.

Amakusa's moves:

Taunt: Heavy Slash or Kick

Force Ball: All four buttons at once.

Kamikaze Bomber: Triangle Jump, then A.

Fire Dragon: Quarter Circle Back, Slash.

Teleport: Quarter Circle Forward, then Slash to go forward or Kick to go back.
Information in this section was contributed by Jesse Smith.

Hint: Defeating Amakusa:
Select Galford or Hanzo. When Amakusa is next to you, do the Triangle Jump and do the Heavy Slash over her head. Repeat this during the entire round time.