Extra Features : if you hold Test Button + PL1 Button 1 during boot, you get extra options in the test menu. 
A level skip, BG test usually etc...

Play As Ayin : at the character selection screen, highlight the [?] and press Up(X3), Down(X3), Up(X7) and Ayin will appear.

The game forbids the initials 'SEX' on the high score table. If you try, it gets changed to 3 smileys, 
and 'THAT all IS all WRONG' appears.