Did I dream this surreal cartoon, part two

Per nevermore’s suggestion, I’m spinning this off of his/her similarly titled thread, hoping that it’ll stand out more (and finally get answered after 30-odd years):

I saw this movie on TV, probably in 1975 or 76. Definitely animated; possibly in 60s/70s anime style (think a Speed Racer-ish look to the characters). The only scene I can recall is of a character on the floor of a large ampitheater-type room (think 18th century med school lecture hall); on tiers rising well above the character’s level are smallish animalistic characters (think Pickachu-looking) that are chanting/laughing (think the laugh in The Beatles’s “I Am the Walrus”). The character on the floor may be transforming into something (perhaps one of the Pickachu-ish things, but definitely something animalistic).

With the mods’s indulgence, one last-ditch effort bump.