9. Dooku Is Ordered To Kill Ventress
One of the most welcome additions to the show, Asajj Ventress was a brutal assassin and the latest apprentice of Separatist leader Count Dooku. Sent on numerous missions in the early seasons and often seen clashing with Anakin and Obi-Wan, she was wildly fun to watch and proved to be a worthy adversary to the core protagonists.
But then, halfway through the third season, everything fans thought they knew about the character was thrown out the window, as she was betrayed by Dooku on the order of Palpatine, who was worried his apprentice would use her to betray him.
In only one scene, Ventress went from ultimate villain to surprisingly sympathetic, left for dead by her master and forced to confront a world where she wasn't at his side.
Throughout the rest of the series, she became a bounty hunter, trained the vicious Savage Opress in hopes of getting revenge on Dooku, and even briefly teamed-up with both Obi-Wan and Ahsoka Tano. An unexpected character development to be sure, but an incredibly welcome one considering where she ended up.