I Am Not Shazam: Felicity Fieldmouse is commonly referred to by fans as Amelia Fieldmouse due to an earlier character that might have been the mother of Morty and Ferdie too. Scuttle is sometimes called Weasel after another henchman of Pete who starred in Disney's Mickey Mouse Adventures series.
The Grey Mouse's schemes. They are always a variation of "let's replace Mickey and make everyone believe he's the imposter, then kill him", and he's damn good at them-In the latest, one of the people he convinced he was the real deal and Mickey the imposter was Mickey Mouse himself.
A two-part retelling of TheStrangeCaseOfDrJekyllAndMrHyde was published, with Mickey as Jekyll and Donald as Hyde. The first time "Donald Hyde" appears on-page, he savagely destroys Huey, Dewey and Luey's market stall. And let's not talk about this◊ image...
So Bad, It's Good: The 2002 story "Invasion of the Killer Penguins". Mouseton gets attacked by giant fish, Mickey is turned into a penguin, grows ostrich legs, has to defend Mouseton against the titular giant penguins, grows giant ears and starts flying... it makes sense in context, sort of. Or not.
What Do You Mean, It Wasn't Made on Drugs?: Bill Walsh's work, especially the later stuff. While Gottfredson's stories leaned towards mystery and adventure, Walsh's preferences were for horror and scifi. There are comics in which he puts those themes to use for a story, like "The House of Mystery" and the early Eega Beeva plots. But there are also comics that are just one long ride of weirdness that eventually reaches an end but not a conclusion. "A Fatal Occupation" and "Mousepotamia", which co-stars Jaq and Gus from Cinderella, are good examples of that. Add to that Walsh's tendency to drop characters that are portrayed as important the moment he's got other ideas, and you get stories like "The Magic Shoe", which spends about a third on Mickey's journey to meet an Irish doctor to help him with his hiccups and then never actually has Mickey meet the doctor as his encounter with the king of The Fair Folk startles him out of it and forms the basis for the remaining two thirds.