luna goes into the everfree, and finds a mysterious pony, but she is not quite what she seems. she is put under the care of twilight, and new mysteries about this strange creature appear. she is definetly not what she seems. as twilight and luna search for clues about this strange creature while keeping it from celestia, they discover some horrifying things.
I'm going to hazard a guess that English isn't your first language?
This is an intriguing start.
There are some minor spelling errors, such as
should be
and
could be something along the lines of
as a few examples.
Overall, you have the setting and details of the story spot on, and you do a great job creating atmosphere and character. All it needs is a bit of clean up, fixing a few errors here and there.