The film opens with the Tennysons (Ben, Gwen, and Grandpa Max) battling a robotic tank in Bellwood. Ben morphs into Upgrade to fight it, but Gwen argues that a magical spell is needed. She casts the spell while Ben is attached to the tank, causing a malfunction in the Omnitrix. The device glows pink, and Ben passes out, waking up in a strange green dreamworld haunted by his own aliens.
: Dialogue surrounding the "dismantling spell" Gwen cast, which accidentally overloaded the Omnitrix with mana. ben 10 destroy all aliens transcript link