NON-CANON:

Return of Revenge Christmas Celebration Animation - This is the Return of Revenge themesong.  As a themesong, it has no real bearing (or even indication) of the plot.  Just watch it.

Destiny - Eggman sings a jovial song about his immunity to lava.  Windows Speech Recognition fails to transcribe the subtitles.




CANON:

Return of Revenge (AKA Robotnik's Revenge):
The very first episode chronciles the conflict of Ninaj and Sonc, as well as Dr. Eggman's very first appearence on Mobiearth.

Return of Revenge Sidestroy B: 
Eggman has defeated Sonc, and now he is free to conquer Mobiearth... or so he thinks, until a mad robot named Zerox, created by the evil Dr. Wilight, shows up with the intent of killing Eggman!

Return of Revenge Episode 3 or 4 or so - Trouble on Super Island!:
The first actual numbered episode unfortunately takes place SEVERAL episodes later than Sidestroy B, leading to a confusing confrontation with Supersonc, Gigantor being a canonical character, and Eggman in an afro.  But could these events lead to a horrific threat being unleashed?