Spinel

Spinel is the main antagonist of Steven Universe: The Movie, and perhaps the most notable instance of the sexywoman phenomenon in Steven Universe, rising in popularity quickly thanks to her tragic backstory, incredibly catchy song, and rubberhose animation aesthetic. She's essentially a modern Harley Quinn.

Basic Information
Once upon a time, Spinel was made to be the "best friend"/entertainer for Pink Diamond, the youngest member of a group of intergalactic dictators known as the Diamonds. This was very nice up until Pink Diamond got her first colony, and decided "yeeeeaaaaah I don't want this clown following me around while I do important business things :/". However, Pink Diamond was an asshole, and decided the best way to resolve the dilemma of "I don't want you to follow me" versus Spinel's desire to follow her was to be like "okay how about you go stand here until I come back okay? okay :)" and when Spinel listened, she proceeded to leave and never look back, fully believing this wouldn't have consequences. And she was right! It didn't! For her. Except the plot of Steven Universe got broadcast across the galaxy, Spinel heard it, aaaaaaand cue the movie.

For more information, visit her page on the Steven Universe wiki.

Theme Song:
"THAT'S RIGHT I HEARD THE STORY OVER AND OVER-"

Dominating
Took out the main Crystal Gems and crippled Steven within the first few minutes of her appearance, and even though that was helped by the element of surprise and the Crystal Gems being a bit rusty when it comes to combat, even without those two things she still puts up a good fight.

Duality:
Between her original happy-go-lucky form and her rage-induced current form. We get to see both sides in equal measure thanks to Spinel getting rejuvenated back to her original state for a good while.

Retro
Distinctly based off rubberhose cartoons, most notably Micky Mouse with her pigtails.

Clown
Served as Pink Diamond's court jester more-or-less; she fits.

(Vriska)ization
Has a good amount of AUs centered around her. Just look up "Spinel AU" and you'll see a variety of humanizations, swap AUs, Crystal Gem AUs, ETC.

Knifemurder
Had absolutely no qualms poofing the Crystal Gems with the rejuvenator. Yes, this technically didn't kill them, but it did do a factory reset, which could arguably be worse. Also, no issues with killing everything on Earth either. That too.

Angst
See the basic information.

Power
See the section on Dominating.

Villain
Serves as one for the Steven Universe movie. However...

Power of Love
Gets redeemed at the end via friendship, as is the norm for most Steven Universe villains.