Phineas and Ferb (2007)

S01E40 The Monster of Phineas-n-Ferbenstein

The boys discover that one of Ferb's ancestors from the Victorian era played a key role in helping a scientist bring a monster to life. At the same time, Doofenshmirtz reminisces about his great-great-grandfather, Dr. Jekyll Doofenshmirtz, sharing the tale of his unique legacy.