Chapter 1: I liked how this story actually had an ulterior motive, the whole meaning within a story is really great and you showed it in a really lovely way.
Key was a really great character but I would have loved to understand more about about Onew who seemed like his back-story could have been really interesting. Did he dare about Taemin? If so then why?
I agree with most of the points that Amalya pointed out, her advice is pretty solid.

The only thing I didn't get is why Taemin's parents treated him differently...how did they treat him before?

Anyway, it was a sweet story and I hope you did well on the competition :)

Chapter 1: - I like the way you set up the context of the story. Good description of Taemin and the mirror as well. I really liked the touch with him not disturbing the dust even though his hand went through it.
- Magic aside, I take it this is no ordinary mirror withstanding Taemin's determined assault. lol Though what kind of place did he fall into? You did good about describing the world, which I loved your nontraditional approach, but was the mirror hanging on a tree? Floating in the air? Something?
- I'm loving your description of Key. heh I can totally see all of it. Though watch the redundancy here: "You might barf out your lunch..." and then you explain again "...on how I would barf my lunch out." You establish it early so you don't need to restate it. His 'boy he wasn't kidding' would suffice. :)
- You do seem to have a way with unexpected twists. I wasn't expecting that about Minho, to be honest, though I don't know why Krystal would have had to marry him anyway.
- I will say that was brilliant of Taemin. I suspect the priest or whoever was marrying them would have seen as well but overall, the cunning! lol
- It was entertaining reading Taemin's escapades in trying to escape for sure, though when he got back, I was very confused by the drastic change in everyone else. Why were his parents fakers? Also, I was unsure why Onew offered to help so easily (tears aside lol). It was definitely useful to have his ability cross over but I'm not sure how that happened or was sustained. And while I absolutely love the message you portray at the end about just being yourself or accepting and liking you for you, I'm surprised no one made the connection between the two Taemins and also that it was no big deal the 'old' one just randomly appeared again after an unspecified amount of time.

(cont...)