The melody comes from The Caretaker's It's Just a Burning Memory, a looped ballroom tune used in his long project about memory loss. Online editors slowed and distorted it for the Mr. Incredible Becoming Uncanny format, in which Mr. Incredible grows progressively more unsettling across phases. Later phases, including phase ten, use harsher, scarier versions to mark the point where the joke turns into horror. That contrast between a warm old tune and a corrupted version is why creators keep returning to it for uncanny edits.