As part of my game, I thought it would be fun to make a hidden level that pays tribute to Mario Bros (one of the earliest games I ever played). It would be themed in that way with 8-bit graphics and question mark blocks and completing the level would say "Thank you but the princess is in another castle" or such.

For the sound track, I'm thinking of just overlaying the standard mario theme music by playing it on a virtual keyboard using a different instrument/timing or something.

My question is, am I legally safe? I'm not using anyone else's actual music, I'm just playing the same tune in a different way myself. Do I have to get licensing for this?