Madam Mim in The Sword in the Stone is cheerful, amiable, and actually pretty friendly when Arthur blunders into her house, and while he can tell she's unpleasant, he doesn't even realize she's dangerous until she tells him she has to kill him which she says with about as much fanfare as someone saying it's suddenly started raining.
Ursula in The Little Mermaid is pretty hilarious, and even when King Triton confronts her about Ariel's Faustian contract she greets him with a, "how are you?"
Cat R. Waul from An American Tail: Fievel Goes West, a cultured, well mannered "gentlecat" who lures New York mice out west in order to turn them all into "mouseburgers", because simply chasing and eating them is an "unnecessary expenditure of calories".
Gru of Despicable Me is gradually softened into this over the course of the story.
Dr. Facilier from The Princess and the Frog. In the words of Prince Naveen, he is "very charismatic". Even when he's manipulating the prince's butler and summoning help from his Friends on the Other Side, he's always polite and cordial. Except when you put his voodoo amuletin danger.
Waternoose from Monsters Inc is legitimately avuncular with Sully, and is sincerely regretful when his plans require trapping him in the human world. He even tells off his Mook for not being half the monster Sully is.
Jumba Jookiba of Lilo & Stitch may constantly boast over his status as an evil genius, and he may have created over 600 super-destructive aliens, but he's a pretty decent and sociable guy overall. He even gets a Heel-Face Turn near the end of the movie.