ITs kinda hard to explain since there is so many characters and different lines to follow, ther is atleast 4 animated series of sonic and a movie, the movie and the first series i want to say is connected in some way, the second series had its own and i want to link it whit the cartoon thats still is published in Archie comics (or on its own i havent figured that out) and it tells that Mobius is earth after some rather interesting bombing (DNA changing bombs ME LIKE).
Then we have Sonic underground a series i don't know much about and i have to still see the second series. All thre of them have splited universes, which allso is the case in Sonic X.
Then we have sonic the comic that is a special case, first they take of official then they go and hit botton and the ship sinks and goes under but continues as the Official unofficial offical magazine.
SOnic the comic online here
Sonic the comic info when it was offline.
ANd the Archie comic info.
Sonic the Hedgehog (comics) - Wikipedia, the free encyclopedia
The second series.
Sonic the Hedgehog (TV series) - Wikipedia, the free encyclopedia
ANy more jsut ask me send a pm or go wikipedia or read the comics....
The only common thing is that Robotnik is in all the series, yes His name is not Eggman, thats based on sonic always calling him eggman.