Reportedly, child actor Billy Mumy, who became famous as Will Robinson on TV's "Lost in Space," was offered the role of Eddie Munster prior to Butch Patrick, but his parents objected to the makeup. He later guest-starred in the Munsters episode "Come Back, Little Googie," playing a brat.

Bonnie Franklin, famous as TV mom Ann Romano in "One Day at a Time," guest-starred on "The Munsters" in one of her earliest television appearances ("Herman's Sorority Caper"). In 1988, ironically, she directed an episode of "The Munsters Today."

Fred Gwynne inherited the Boris Karloff appearance twice in his career, first as a Frankenstein's monster look-alike in "The Munsters" and later in the 1969 ABC-TV movie version of "Arsenic and Old Lace," made up as Karloff by makeup artist Dick Smith. Gwynne murders someone in the movie and remarks, "I killed him because he said I looked like the Frankenstein monster."

"The Munsters" and "The Addams Family" debuted within a week of each
other and two years later got axed in the same week.

Although they are both remembered for playing Marilyn Munster, Beverley
Owen and Pat Priest have never met.

Butch Patrick, who played Eddie Munster, later played Pugsley in a 1971
CBS-TV special, "The Addams Family Funhouse," which included Stubby Kaye
as Uncle Fester, Pat McCormick as Lurch, Jack Riley as Gomez, and Liz
Torres as Morticia.

(Source: THE MUNSTERS, by Stephen Cox)

[Has anyone seen THE ADDAMS FAMILY FUNHOUSE?? I don't remember
that TV special at all.]