Spicy Stir is daughter of the Mistress of the Other Side, alicorn of the afterlife.
She's very optimistic, energetic, likes extreme things, thinks that everything in life should be tried at least once. And if some of the things she tried send her back to mom - well, it's just a mild inconvenience, the next day she will respawn in a new body, fresh and healthy!

Her mom raised Spicy Stir as a proper princess of the afterlife kingdom, she had the best teachers teach her manners, chess, calculus, magic, dancing, poise, eloquence, etiquet, her pokerface was made perfect, better than Celestia's (according to the Spicy Stir's mom, of course)... and when Spicy Stir hit puberty all that was thrown out of the window. She craved freedom, life, playfulness, everything that princess of the her mom's kingdom lacked. And, although Mistress of the Other Side was quite shocked and didn't understood such weird wishes, she deeply loved her daughter and accepted her as she is. She let her go to the world of living. But before that she helped her craft the rune script that let her hop between the world of living and the world of dead by reconstructing her body in the place where she enters the living world. They workedon that runescript together, and integrated it into the Spicy Stir's very soul. From that work Spicy Stir gained her cutie mark.

Now, in the living world, she experiments to her heart's content. Some of her experiments shocks other ponies, like the one when she killed herself and the next day came back to try her own meat, but she has good heart and don't wish anybody harm, physical or emotional.

One of the new experiences she had was love. Now she and Solid_Punch are happily married couple, and he sometimes assist her in her experiments. Also, he helped her understand the impact her experiments have on others, and explained how many things in life work. Especially how pony society works. So now the experiments of Spicy Stir are much milder and less publically watchable.