Ratigan kills a drunk mouse for calling him a "rat."
"Oh, my dear Bartholomew, I'm afraid that you've gone and upset me. You know what happens when someone upsets me..."
Also, Ratigan verbal-owning Basil. Vincent Price's maliciously cheerful voice makes it all the more awesome.
"Frankly, I expected you fifteen minutes earlier. Trouble with the chemistry set, old boy?"
"You have no idea what a delightful dilemma it was, trying to decide on the most apporpriate method for your demise. I had so many ingenious ideas, I didn't know which to choose! So... I decided... to use them all."
Ratigan deserves one for listening to Basil press his Berserk Button and, judging by the look on his face, taking a lot of self-control not to jump on Basil and maul him right there.
"Ratigan, no-one can have a higher opinion of you than I do... and I think you're a slimy, contemptible sewer rat!"
Ratigan threatens to feed Flaversham to Felicia if he doesn't finish the Queen robot in time. Flaversham then becomes so angry that he manhandles the in-progress robot in a way that causes it to squirt oil on Ratigan's coat. The following line ensues.
"You can do what you want with me! I won't be a part of this-this-this evil any longer!"
Becomes a heartwarming moment combined with tearjerker when Ratigan realizes that Flaversham really is willing to die rather than commit this crime...and so instead threatens the life of his daughter, after which Flaversham complies with Ratigan's demands.
"SEWER RAT!" Complete with a finger-point that Phoenix Wright himself would be proud of. It's a potent mix of Awesome, Heartwarming and Funny. Basil taking control of the robot queen and using it to give Ratigan a blistering"The Reason You Suck" Speech while making the robot expose itself as such, Olivia happily reuniting with her father, and Dawson and even the Queen tying up Ratigan's henchman.
The ending of the movie: not only did they play up the Reichenbach Falls story (complete with a Disney Death for their Holmes stand-in), but the way the movie changes from a madcap, comedic mystery into a breathtaking chase sequence, a climactic fight inside the Clock Tower of Parliament, the Nightmare Fuel of Ratigan's evil transformation into a crazed killer rat, and finally Basil's clever usage of Big Ben striking to topple the villain to his death (all of it with a very effective musical score) is simply incredible. Most people who talk about the Disney Renaissance say it began with The Little Mermaid, but just as many contend that The Great Mouse Detective should be the real beginning, or at least that the seeds of it were planted here. (The movie, while vastly entertaining, does perhaps pale a bit compared to what followed it.) This ending sequence may be one reason why it deserves such an inclusion.
Plus, that sequence marked the first time CGI was used by the feature animation department. The gears were computer animated then traced by hand.
Don't forget when she bit him on the hand during the clock tower chase.
Some credit to Fidget. He's a clever little bat, turning the toy store into a gauntlet as soon as he found out Basil was there, managing to escape and snatch Olivia away in the process. And though you wouldn't think it awesome, he lasted for a good while with Felicia trying to eat him before Ratigan called her off. He was probably the one who put up the biggest fight against her out of everyone she's ever eaten.
Though Ratigan's schemes such as the Big Ben Caper were rather impressive to begin with and earned him a lot of money, he manages to outdo himself when he comes up with a scheme that will make him become the supreme ruler of all mousedom.