Codename Kids Next Door (2002)

It is a sad day in the treehouse, when Chubbo, one of the KND's power-providing hamsters passes away; and it is saddest for the overly sensitive Numbuh 3, who even maintains a vigil at his grave until the weather proves inclement. But unwise is the one who mourns too long for the dead, because during the dark and stormy night, a gang of ghostly hamster arrive, and drag the terrified Three to the hamster afterlife! Now the team must penetrate the very netherworld to rescue their friend, but can even the KND overcome a mob of restless rodents?!