Batman [Model DMG-BAA]

Sound test:
At the title screen, hold Up + Right, then press Start.

Level and weapon select:
Beat the game once, then at the title screen press Start to begin a new game, but before the title screen disappear, hold Select. Additionally, when the final message of the credits roll "THE END" appears, hold Select and wait for the title screen. This will also enable a Weapon select mode. During the game press Select to cycle between all possible weapons.

Batwing shot rate select:
During the Batwing stages (3-1, 3-2), press Start to pause the game, then press B, Up, Select, A. Now, you need to input a 4-button sequence, which will be treated as 4-bit binary number, which is representing a desired shoot rate when you hold A during the game. Any buttons except A means binary 0, the A button means binary 1. Lets use for the binary 0 the B button, then we can write down all possible valid codes in the table below. So, the best complete button code of this pause cheat for fastest shot rate is B, Up, Select, A, B, B, A, A. Now, just unpause the game.
B, B, B, B - Invalid value, set to shot rate 15 (slowest) instead 0.
B, B, B, A - Invalid values, set to shot rate 10 (default, used by the game) instead 1 and 2 correspondingly.
B, B, A, B
B, B, A, A - All valid values from 3 (fastest) to 15 (slowest) correspondingly.
B, A, B, B
B, A, B, A
B, A, A, B
B, A, A, A
A, B, B, B
A, B, B, A
A, B, A, B
A, B, A, A
A, A, B, B
A, A, B, A
A, A, A, B
A, A, A, A