With Maltazard now seven feet tall and Arthur still two inches small, our hero must find a way to grow back to his normal size and stop the Evil M once and for all, with the help of Selenia and Betameche.
| Actor | Role |
|---|---|
 Freddie HighmoreArthur Montgomery | Arthur Montgomery |
 Mia FarrowGranny | Granny |
 Robert StantonArmand | Armand |
 Penny BalfourRose Montgomery | Rose Montgomery |
 David GasmanThe Mechanic | The Mechanic |
 Antony HicklingDouglas | Douglas |
 Dashiell EavesSimon | Simon |
 Joseph RezwinBrad | Brad |
| CCooper DanielsGeorge Lucas | George Lucas |
 Ron CrawfordArchibald | Archibald |
 Stuart RudinFrancis | Francis |
 Steve RoutmanDr. Stitch | Dr. Stitch |
 Peter HudsonGeneral Montgomery | General Montgomery |
 Lou ReedMaltazard (voice) | Maltazard (voice) |
 Selena GomezSelenia (voice) | Selenia (voice) |
 Iggy PopDarkos (voice) | Darkos (voice) |
 Mike PowersGrafitti Artist (voice) | Grafitti Artist (voice) |
 James A. BafficoMartin Baltimore (voice) | Martin Baltimore (voice) |
| JJean Bejote NjambaBogo Chief | Bogo Chief |
| LLaurent MendyBogo | Bogo |
| NNorman StokleMayor | Mayor |