I don't even know this fandom and I can already spot the mistakes. I had to re-read some parts because of the grammar! And the lyrics felt...awkwardly placed. Very awkwardly placed.

What have you done to Dean? What have you done to Sam?! Good grief, the only IC part of this fic was Dean and Sam caring about each other! I mean, I like Sabriel as well as the next person, but this pretty much just stomped on everyone's characterization, Dean's most painfully (imo). Kill it, please (once you have permission, of course).
~DF

I'm a pretty heavy Sabriel 'shipper myself, but this... Hnggh. Where do I even begin...

Just to avoid any further confusion.

...I get really confused and automatically think of the Garth Nix novel by the same name.)

I dunno about Sabriel being a bad ship- I, personally, think it has a neat dynamic, and since when has canonical loathing stopped shippers?- but oh man, poor Sam. That is as OOC as OOC can be. Dean less so, but definitely still slipping into OOC territory.

Whenever you get permission, I say forge on ahead with it. Stake a claim on the "claimed badfic" page on the wiki.