Press Up, Right, Down, Left, Up, Right, Down, Left at the 'Difficulty' menu and the player skulls feature will become available in Arcade mode.
At the Main menu enter the following codes for the corresponding gravity effect.
Press Down, Down, Down, Down, Right, Left, Right, Left.
Press Up, Up, Left, Left, Up, Up, Right, Right.
At the 'Difficulty' selection screen of 1-Player Arcade mode press 'Down' 10 times to make the cursor move automatically under the Master difficulty and automatically start the game in Savant mode.