Here are most of the enemies/villains in Sonic:    


1. Mephiles the Dark
    2. Mammoth Mogul
    3. Dr. Robotnik
    4. Eggman Nega
    5. Eggman Empire
    6. Suppression Squad
    7. Patch
    8. Scourge
    9. Dimitri the Echidna
    10. Finitevus
    11. Fiona Fox
    12. Princess Alicia
    13. Miles
    14. Anti-Boomer
    15. Rosy The Rascal
    16. Black Doom
    17. Snively
    18. Lien-Da
    19. Drago
    20. Destructix
    21. Lightning Lynx
    22. Sergeant Simian
    23. Predator Hawk
    24. Flying Frog
    25. sitaw the Dynamite
    26. Bark the Polarbear
    27. Fang the Sniper
    28. Scratch
    29. Grounder
    30. Coconuts
    31. Chaos
    32. Metal Sonic
    33. Metal Scourge
    34. Dark Gaia
    35. Luna
36. Lavinia
    37. Heavy
38. Bomb
    39.Ixis Naugus

I hope you enjoyed reading. XD