Here is a remix of Boss theme from Sonic & Knuckles. Completed with Beginner, Normal and Eggman diffuculties.

edit:fixed Normal and Hard difficulties to Rolled's suggestions.

And if you're willing to go for a challenge, I present The Eggman's Challenge (that is not to be played!!). (If you want it, it is in the sixth post of the first page of this beatmap's thread.)
Simply move the osu file into the the song's folder.
There may be a few timing issues there and one part which I put notes randomly around that I need to fix still (and too lazy), marked by the bookmarks.