Post a fictional character who appeared only once in a TV show & see if anyone knows the show W/O using Google

[Wiz Imp]

27. Chuckles did not physically appear in the "Chuckles Bites The Dust" episode

However, he did appear in 3 separate episodes.

Chuckles's first on-camera appearance was in the episode "The Snow Must Go On", originally broadcast November 7, 1970. Richard Schaal portrays Chuckles when he arrives at TV station WJM the morning after a city election, to find the news staff —having lost contact with City Hall during a blizzard— still on the air. Chuckles has the election results in his newspaper, and announces the winner of the mayoral race on the air in clown character.

In season 3, Chuckles had a brief non-speaking role in the third season episode, titled "Who's in Charge Here?", where he was portrayed by an uncredited extra. In this episode, Chuckles meets with Lou Grant, who has been temporarily promoted to WJM's program manager. Chuckles is seen arriving for the meeting in full clown makeup. Mark Gordon next played Chuckles in "Son of 'But, Seriously Folks'"; aside from these appearances, Chuckles, like Phyllis Lindstrom's husband Lars, existed only off-stage.

He was referred to numerous other times but not seen.

https://clownopedia.fandom.com/wiki/Chuckles