Don't know if this is well known(Classic Music)

[Cibernetico]

Not that people play MK for the soundtrack, but during the stage selection, if you press start on some of them, you will get the Shao Kahn evil laugh and it will play the stage with the classic music enabled without the need to input the kombat code.

 

[SkyratiK]

If you press start when you select your costume instead of A/X it picks the secondary color scheme for that costume too.

 

[Gesture Required Ahead]

It's not a glitch and yes, it's well known. Since the demo came out actually.