You ever think to yourself 'Gee, I wonder what I'll do for a certain night filled with candied treats and scary things like ghost, monsters, colts and fillies dressed as silly creatures, and the like?' Well thats what lil miss Dashie wanted to do. At first. She grows tired of the same ol' thing year in and year out. Now she wants to do something different. Something adventurous. Something spectacularly awesome.
Something like an abandoned house said to hold a terrifying secret along with its equally terrifying tenant. Nopony goes to this house out of fear of its reputation to turn the toughest of stallions into terrified fillies screaming for mama. Its rumored this is the house responsible for giving a certain pony the 'derps'. Anypony with half a brain would stay away from such a spooky mansion of spookiness.
Enter Rainbow Dash. And.... Spike?
Why? Because why. Thats why.
For the Halloween SpikeDash competition. Because imma win. Thats why too. Rock on.
A contest entry entry huh? Awright, I'mma tell you what to improve (just minor spelling issues though.)
The usage of "they're" and "their" is as follows:
"They're" is "they are" and "their" is when something belongs to "them"
A key thing I always bear in mind is when an apostrophe is used, I try to split the words and see if they fit.
E.g.
would become
hence, "their" should've been used.
Next up is the use of "tree's" or "trees".
Plural of the word "tree" is "trees" (without the apostrophe) while "tree's" means "tree is"
You also seem inconsistent with the plural of "hoof," which should be "hooves" (but you DID use that too... so you maybe just forgot some?)
Just grammar nitpicks from me. Although I will also say this: be careful about author comments in the story itself/breaking the fourth wall. It can clog the flow of your story.
Story-wise I can't give you any advice, since I'm not very good at that myself
Keep writing and I'll keep reading!
SCWEEEET
My first official critique!
I shall improve, just because you told me to do so.
Thank you
I better have won the contest thingamajig, or atleast got second place....meh
Awww, yeah; SpikeDash!
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I'm debating about how to ship these two. They will start off as friends. After that is anyone, but mines, guess.
Just going by the description I can see this as a scooby-doo spoof with rainbow actually getting scared and spike protecting her and the bad guys are the three pegasus jerks from flight camp.
Followed by a real ghost that just wants ponies to let him rest and stop trespassing.
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a mix between scooby doo and paranormal activity rather. no real bad guys... that i can think of anyway
Come on!
Soooooo I'm looking at this and I should be updated and DONE with it by halloween.
IF I feel as though people actaully read it.
I seriously thought this was deleted. But after some time looking for it, I have FINALLY found this story!!!!!!.
Buuuuuut it's on hiatus. 
Though I still hope you will finish this in the future.
Yessir, this will continue in betweeen a week to a month. Really, I want to finish this before the night of the spookies