These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Canon Fodder: Perhaps due to its status as one of the few Disney movies not to be given an unneeded sequel, it has a bustling fan fiction community, some stories of which are mouse-ified re-tellings of Sherlock Holmes stories.
Crazy Awesome: Basil. His introduction involves him racing in to his apartment in a huge Chinese costume, shooting his pillows, giving a Big "NO!" when the bullets don't match up, and then playing his violin dramatically. And that's not even getting into the trap scene later.
Ensemble Darkhorse: Fidget (so much so that a comic story in the last issue of Disney Adventures inexplicably brought him Back from the Dead and turned him into a sidekick to Olivia). No few animation, film, and comic magazines during the time of the film's original release and re-release had reviews and articles questioning why "the big dog" was pushed so heavily in the advertising when it was the bat that who most audiences came away remembering.
Ratigan, for Disney Villains. He isn't featured in the merchandise as much as other Disney villains, but he still has tons of fans.
Foe Yay: Basil keeps a portrait of Ratigan, his Arch-Enemy, whom he obsessively pursues, in his room for one thing...and Ratigan has a voodoo doll of Basil on his shelf. Sure, it has pins in it, but who do you think made the doll, hmmm? Disney did release this◊, after all...
Ratigan's "Goodbye So Soon" song reeks of this, as well as the almost fliratious way he says "Bye bye, Basil" as he leaves Basil and Dawson to die in his Death Trap while the song is playing.
Ratigan also playfully pinches Flaversham's cheek and almost kisses him.
Thanks to the Square/Cube Law, Ratigan is actually very likely to have survived his Disney Villain Death. And if he landed in water? Rats can tread water for as long as 3 days.
Germans Love David Hasselhoff: Comics about Basil are very popular in the Netherlands. But Dutch Disney comics tend to feature relatively obscure Disney characters anyway - a good 50% of the weekly comics are about Bre'r Rabbit, Madame Mim, Hiawatha, Panchito, or Horace Horseshoe.
Getting Crap Past the Radar: Seriously, there is no other explanation for how a burlesque show got into a kid's film than "the Censors were drunk-on-duty or out of coffee".
Glurge: It can be very hard to watch Olivia and Flavisham's reunion owing to how cringe-worthily tooth-rotting it is. Especially since they're carrying on like that in front of the Big Bad.
Ho Yay: No such thing as a Holmes adaptation without it.
Love to Hate: Ratigan, mainly due to Vincent Price's love of hamming it up.
Magnificent Bastard: "The nefarious Professor Ratigan! He's a genius! Twisted for evil! The Napoleon of Crime! There's no evil scheme he wouldn't concoct! No depravity he wouldn't commit! Who knows what he is up to even as we speak?" And if Tv Tropes type any more exclamation marks, the server will explode!
Moment Of Awesome: The escape from Ratigan's trap, capped by their posing for the camera ("Smile, everyone!").
Mondegreen: The lyric "I'll take off all my blues" in the song "Let Me Be Good To You" has reported to have occasionally been misheard as "I'll take off all my clothes". (Granted, who could blame those who misheard the line? All the clothes Miss Kitty is wearing are BLUE.)
It doesn't help that she says the line in question while whipping her skirt off to reveal a one-piece dancer's outfit.
Vindicated by History: Overshadowed in the 80's by Don Bluth's An American Tail, and for awhile was overlooked or lumped together with the other films of the Dark Age. Now it's fondly remembered as ones of the films which reinvigorated Disney Animation.