Fluttershmooze is a hybrid of the time space goop from the Undertale au coolskeleton59 and fluttershy. it was created by me and the coolskeleton59 discord server!
Basically: this goop feeds off of pony energy and possesses their victims. Fluttershy ended up in the everfree forest because one of the animals ran away, and her hoof got stuck on a spiky branch. She started bleeding and the goop, that was possessing the animal that ran, smelt the blood and possessed Fluttershy.