This very weird animated feature from 1975 takes the following tack:

1. Take the most well-known operettas of Gilbert and Sullivan (along with a few of their lesser-known ones) and throw their plots and characters in a blender.
2. Turn what comes out into an animated musical.
3. Get British cartoonist Ronald Searle, who has a broadly caricaturist style, to design it and oversee the animation.
4. Re-write most of the lyrics and arrange them in an EXTREMELY 1970s pop style.
5. Somehow expect this to appeal to people.

It's not that the idea of a Gilbert-and-Sullivan-themed animated musical is BAD in and of itself...if it had focused on adapting a single work, and had a more appealing visual style. (Ronald Searle's style is very good for newspaper cartoons, illustrations, and the opening credits of the movie musical Scrooge, but in animation, it looks ugly and off-putting.) Plus, throwing Every. Single. Gilbert. And. Sullivan. Character. EVER. into the same plot, not to mention cobbling together said plot from all these different works, makes the whole thing look entirely too overstuffed. It's amazing that Bill Melendez, who directed the Peanuts specials which are known for being simple and straightforward, helmed THIS. And those 1970s orchestrations...ai-yi-yi!!! (Unfortunately, this wasn't the last time G & S would be warped onscreen...The Pirate Movie came along seven years later.)

This review from Musical H-E-L-L, a YouTube series that slams on awful filmed musicals, gives you an idea of what to expect. https://www.youtube.com/watch?v=tlpl8uPECS8&t=321s&ab_channel=MusicalHell

(It seems that the filter won't print a certain nickname for Richard, so I had to edit the title.)