| Ep # | Title | Key Alien Debut | |------|-------|----------------| | 1 | And Then There Were 10 | Heatblast, Wildmutt, Diamondhead, XLR8, Grey Matter, Four Arms, Stinkfly, Ripjaws, Upgrade, Ghostfreak | | 2 | Washington B.C. | – | | 3 | The Krakken | – | | 4 | Permanent Retirement | – | | 5 | Hunted | – | | 6 | Tourist Trap | – | | 7 | Kevin 11 | Kevin Levin (mutant) | | 8 | The Alliance | – | | 9 | Last Laugh | – | | 10 | Lucky Girl | Gwen as "Lucky Girl" | | 11 | A Small Problem | – | | 12 | Side Effects | – | | 13 | Secrets | Master Control, Vilgax |
: 27, 31–32, 34, 39. Season 4 – Final Episodes & Setup for Alien Force (Episodes 40–52) Lighter tone, more filler, but includes series finale. ben 10 episodes
| Ep # | Title | |------|-------| | 40 | Perfect Day | | 41 | Undercover | | 42 | The Unnaturals | | 43 | Monster Weather | | 44 | The Soda Popinski | | 45 | Ben 10: Destroy All Aliens (movie – canon) | | 46 | Ken 10 (Ben’s son) | | 47 | Ben 10: Race Against Time (live-action movie – alternate timeline) | | 48–52 | Goodbye and Good Riddance (alternate ending – non-canon) | | Ep # | Title | Key Alien
: 18, 24, 26. Season 3 – The Negative 10 & New Aliens (Episodes 27–39) Ben unlocks new aliens (Cannonbolt, Wildvine, Upchuck, Ditto, Eye Guy, Way Big). | Ep # | Title | |------|-------| |