As Hex seeks the famous Fountain of Youth to restore his youth and thereby his magic, the Tennysons happen upon its presence by accident. Grandpa Max falls into a vat of it at a fair, splashing Ben. While their physical ages revert, so do their mental and behavioral ages, with Grandpa Max wanting to goof around all day while Ben becomes a whiny brat in need of a nap (with all his Omnitrix aliens becoming crabby little kids as well). Will it be enough to stop Hex from gaining the fountain?
—statmanjeff