Casino Night has a 50's style Jazz song, Emerald Hill has a first level sounding song (with the glimmering cresendo at the start that is like Green Hill and Palmtree Panic a topos of Sonic opening levels at the time).

I know this is very speculative, but the 2 Player music seems to go too well with the level themes to be a coincidence.

Again, it makes more sense going with 2 Player Casino Night. I find it a bid odd that Oil Ocean was ever intended to use a 50's style Jazz inspired song. Might be a special case due to it not being a regular level but more of a game mode. Click to expand.Still, kind of a really big coincidence that it was added to the same slot where the Special Stage music used to be in Sonic 1: Sonic 1/Sonic 2 Nick Arcade