To name a few musical horrors:
Sweeney Todd, Anna and the Apocalypse, Rocky Horror Picture Show.

Also, not quite a recommendation - but I found a list of comedy horror movies on wikipedia and have decided to go on an adventure to find the worst ones through titles and brief descriptions alone this halloween: https://en.wikipedia.org/wiki/List_of_comedy_horror_films

Assault of the Killer Bimbos, Dr. Caligari (which is suppose to be an 'erotic' sequel to The Cabinet of Dr Caligari), I bought a Vampire Motorcycle and Evil Toons seem like good contenders so far :D