The New Addams Family (1998)

S1E34 Close Encounters of the Addams Kind

Aliens on a quest for a power source pinpoint the Addams family home as the location. To blend in, they study 1970s television shows and disguise themselves as Greg and Marsha Brady. Once at the Addams residence, they realize Uncle Fester is the vital energy source they seek. To claim him, they challenge Morticia and Gomez to a dance-off. Although Greg and Marsha don’t win, they present their situation, prompting Gomez to devise a clever alternative solution.