Musical bundle train (lvl 1+) (Stops Dec 24th)

Well hello my dear fellow SteamGifters! I think it's about time to get rid of all the bundle keys I've got lying around...

As usual it's a musical train so if you're level 1 or higher and want to board the train, please solve a quick puzzle, jump on board and rock out!

(Note: the answer may well be more than 1 word)