Hmm great villains of disney. They say big things come in small packages, so honorable mention to one who doesn't let their looks stop them from being evil is the master of evil, the prince of destruction, the dark lord Chuckles the Silly Piggy from Dave the Barbarian.
Though another was even smaller, more competent and actually one at a point in takeing over the world, that is DOR-15 from Meet the Robinsons.
Next Ursula of The Little Mermaid, she manipulates the princess, mind controls a prince, uses said princes to turn the king into a worm to add to her very large amount of other victims, and turns into a godly giant monster.
For basiclly owning evil is Malificent from Sleeping Beauty, also in the Kingdom Hearts series she keeps her dark image.
And I guess best evil henchmen villain would be Shego, she is probably the most competent villain on the show, and unlike other henchmen, she rarely makes a mistake, plus her additude is funny, actually pointing out the problems in evil plans.
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Through dream I travel, at lantern's call
To consume the flames of a kingdom's fall