When four aimless rogues all conveniently meet in Trottingham and are immediately confronted with untold dark powers, can they work together to keep the city from being destroyed? Can a showmare, a bully, and two con artists overcome their differences to save the town's residents? Can Trixie, Flim, Flam, and Gilda work together to save Trottingham from...the Headless Horse!
Note: Despite using it a screencap for cover art, this story was written before "Sleepless In Ponyville." aired.
So you wanted a bit of a review, eh? Well, here are a couple of things I noticed.
If the narrator is contradicting their own statements it makes them sound sarcastic or off-handed, giving the mood a sort of levity that can counter a brooding atmosphere. Some of your grammar is a bit off ("Except" right at the beginning of a sentence for example) and you could stand to smooth sentences out a bit to improve the flow. Using a thesaurus might help too.
Could be:
This is the same thing with fewer words. I think it flows a bit better, and by calling the trees an "army" and "inscrutable" we establish from the get-go that this forest is not exactly a friendly place.
We don't know they're creepy or owl filled yet, we only know that they're dark. Given that you cover all of this again almost immediately after, and actually give Trixie's thoughts/reactions/observations, you could probably remove this bit.
Sentences like this are what I call "tell" style. It states the facts as facts but doesn't build atmosphere very much.
This is what I call the "show" style. See how I just described what the sounds were and let you decide what they meant?
This? This is better, but right in between...
I have to say, this bugged me quite a bit.
When a character swears it can tell us a bit about them, like whether they are foul mouthed, religious, naive, a kid, etc. You can go from Lil'Pip's Celestia's Flaming Orgasms (which tells us she's foulmouthed and usually means that she's been surprised by something that wants to kill her, and not necessarily slowly), pass Applejack's "Aw shewt" (relatively polite, and showing mild disappointment) and move on to Rainbow Dash's "For Celestia's Sake!" (invoking a higher power and displaying extreme exasperation). That she "swore swearing words" communicates nothing about who Trixie is as a character, except that she either knows more words that the narrator is willing to expound upon or she's about to start making a vow. If you're not going to put what exactly it was she swore, then just say "she swore at the bell for startling her".
So to wrap things up, "Show rather than Tell" is one style that could be used to improve the flow and build some atmosphere. When we're stuck in a dark spooky place it's the details that get us, so be descriptive.
Trixe tries to off herself almost right off the bat? I can only imagine what she'll do when things start getting SCARY. If the fish could swim away, she probably should have tried the same.
Flim, Flam, and a Trixie Bandwagon, huh? Lots of potential there for personality conflicts leading to throwing each other under the bus, technique transactions, or new and unlikely friendships. Probably the latter, seeing how nice all three are being to the first strangers they meet. Other than that, they all seem pretty in character, which is good.