Tekken

Player Costume Change:
At the Character Select screen, press Square + Triangle for Costume 1 or X + Circle for Costume 2.

Play as Devil Kazuya: Beat all the rounds of Galaxian.
Play as Heihachi:     Beat the entire game without continuing.
Play as Sub-Boss:     Beat the Sub-Boss and he'll be available.

Play Galaga with Two Ships:
During Power-UP, hold Up + L1 + Triangle + X on the player two controller.
- or -
Press Select, and before Galaga round, hold Up + Triangle + Square + R1 until the round starts.

 