Hello readers! I am beginning to start writing again, but it is slow going. I am also editing existing chapters, so give me your ideas!

A strange beast, never before heard of, is roaming the ever-free forest, but the strange part, is he transforms into the ponies he encounters, after being hit with a black dart. Along with the appearance of the pony he becomes, he even gains that pony's magic and special talent, and adds them to his own.
first story, not that good, I know. that's why I need you guys to help me make it better. any problem you find, even if it was already found or mentioned, tell me in the comments. Feel free to nit-pick.
I am also looking for a co-writer. I want to continue this story, but need something new to add to it, more specifically, ideas.
I could use a cover, a picture of Felidae will do.