Sweetie Belle is a secondary character in My Little Pony: Frendship is Magic, as well as one of the main characters in Something Sweet to Bite. She is one of the ponies indirectly responisible for the ressurection of The Candy Mare, the main antagonist of the series.
As a pony, Sweetie Belle is a white unicorn filly, with purple and pink, curly hair and emerald green eyes.
As a candy ghoul, her body took on a more melty appearance with large gumdrop eyes and is fused to Scootaloo.
About a week before Nightmare Night, while helping Pinkie Pie decorate the post office in Ponyville for Nightmare Night, she talks to her friends Apple Bloom and Scootaloo, about how much candy their going to collect on Nightmare Night and how much they'll leave for Nightmare Moon. This prompts the attention of Diamond Tiara and Silver Spoon, who berate them for leaving their candy, stating that they didn't leave any last year. This enrages her and Apple Bloom then states that they aren't going to leave any this year either, Apple Bloom then makes a bet with them on who can make more candy this year.
Later that day when the group goes to decorate the library, she accidentally knock over a bookshelf, after getting into an argument with Diamond Tiara, gaining the attention of Twilight Sparkle. After Pinkie explained what they were arguing about to Twilight, she then finds out how they aren't gonna leave candy this for Nightmare Moon this year. Twilght then explains that leaving candy for Nightmare Moon is a tradition and that it shouldn't be broken, but then after hearing from Diamond that they didn't leave any candy last year either, she realizes that they're is no consequences to not leaving candy for Nightmare Moon. Pinkie then shows them a book called "Ye Olde Tricks and Treats" a book containing several Nightmare Night stories to which she and Twilight start fighting over causing the book to rip in half and have several pages to fall out. While the group leaves Sweetie Belle notices several pages of the book that had fallen out and stuffs them into her bag before leaving.
Resurrecting the Candy Mare
On the day before Nightmare Night, she and Scootaloo were making candy at Sugarcube Corner, with the help of Pinkie Pie. Sweetie apparently having only now begginning to help as she was too busy helping her sister, Rarity make costumes for Nightmare Night.
While Sweetie was busy looking over one the pages that she had out, when Twilight came in and saw it. This startled Sweetie Belle causing her to accidently fling the pages everywhere, showing they were stolen from the book.
Scootaloo finally confessed that they were making candy for the bet they made with Diamond Tiara and Silver Spoon.
Pinkie suddenly starts gathering the candy up, saying they need to take it to the Nightmare Moon statue in the Everfree Forest, Twilight is confused at first, until she gets a look at the title of the recipes and says "Candy Mare" and immediatly helps Pinkie gather the candy.
Scootaloo then asks who the Candy Mare is and Twilight explains the story from the book, the candy was made by an evil candy maker, who kidnapped foals to try his treats and that one of them become a mosnter known as the Candy Mare, a monster who feeds off ponies and who was banished by Luna, by purifying her and turning her into candy. She also explains that the candy itself was prohibited from being made in equestria, so they need to take it to the statue of Nightmare Moon, because it's surrounded by residual magic that acts as a purification spell and in order to purify it and make it safe to eat.
The Ponyville Massacre
The next day, On Nightmare Night day, Sweetie Belle and Scootaloo in their costumes (Scootaloo going as Mare-Do-Well and Sweetie going as a robot), are riding Scootaloo's scooter over to Sweet Apple Acres to tell Apple Bloom the bad news.
Scootaloo is upset they can't trick or treat, meaning they're going to lose the bet, however Sweetie Belle states that the upside is that their will be no candy for Diamond Tiara and Silver Spoon to get.
When they get to Sweet Apple Acres they find the place deserted and when they come up to the door of Apple Bloom's house no one answers. Scootaloo calls out for her and Applejack, only getting no response. Suddenly, they hear a sound and look over to see the door to the barn opening.
The two go over to the barn, to find a pile of ashes and several parts broken, inlcuding the hinges of the door. Scootaloo calls into it, asking if anybody was there. She then hears what sounds like Applejack replying back to her, only distant and hollow. The figure in question started moving closer, as Sweetie Belle asks where Apple Bloom is.
Applejack replies that she's in there with her, stating that they're making caramel apples and asks if they want some. Scootaloo denies, stating they only want to see Apple Bloom. Applejack then states she'll go get Apple Bloom and she retreats and soon a voice that sounds like Apple Bloom's appears, complete with a figure with a red bow.
Scootaloo and Sweetie Belle then explain to Apple Bloom, about how Twilight and Pinkie found out about what they doing and the punishment they recieved. Scootaloo then asks if Apple Bloom is upset. Apple Bloom ask why she would be upset, stating they can still spend Nightmare Night together and like Applejack, also asks her two friends to come inside the barn.
They declined again and state they need to go, to which Apple Bloom replies the she still needs to put on her costume and asks the two help her. Sweetie Belle then asks why does she want them to come inside the barn as she and Scootaloo start backing away from the barn.
Suddenly Apple Bloom floated a few feet in the air, before sticking her head out, revealing it to be severed with her eyes missing and her face covered in caramel with blood dripping from her mouth. Both fillies screamed at the sight, as the decapitated head of Apple Bloom continued to laugh and scream.
The two turn and run away and before getting on Scootaloo's scooter and heading to Golden Oaks Libray to tell Twilight what they saw. After getting there and explaining about what they saw, Twilight then states they to tell someone of authority, so they decide to go tell Mayor Mare.
The group find Mayor Mare at a dance party in town square, but she and everyone else just laughs and believes it's part of a prank. The Candy Mare then appears and starts a massacre killing several ponies. Twilight along with several other unicorns manage to stop her by using their magic to strip her flesh from her bones.
The Candy Mare then attempts to kill Twilight by launching her skull at her only for Pinkie to leap up and smash it with her forelegs, revealing gummy brains on the inside. Her remains then start to form back together, as Pinkie then states the only way to get rid of her is to eat her remains as she starts devoring the Candy Mare, with Sweetie Belle and the others joining.
Death and Transformation
After they were done, the four of them headed back to Twilight's house. There, Twilight takes them up to her room to put them to bed, there the two started crying over witnessing all the bloodshed that happened that night, Twilight then stayed with them until the two eventually cried themselves to sleep.
At some point while they slept, the two transformed into a single gelatinous monster with gumdrop eyes. The transformed duo were then discovered by Twilight who ran in there to save them, as an also transformed Pinkie and Rarity was close behind. As Twilight herself starts transforming, she allows the other monsters to eat her so she doesn't become like them, only to ultimately transform as the four ghouls started eating her.
The two then proceed to join the Candy Mare's army, as they invade Canterlot and kidnap Princess Luna.