**The film's co-Directors toyed with the idea of making Dragon into a pegasus but ultimately decided against it because it didn't really add anything to the film to see her transform.**

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Quoting from the [Director's Audio Commentary][2] (between co-directors Kelly Asbury and Conrad Vernon):

> *We worked on that a loooong time. I mean, how do we show that that potion affects Fiona as well as Shrek? I mean yeah, big blue flash, yeah one flash. I think there was one point, because Donkey was, Donkey changes into a "noble steed", everyone asks, yeah but we asked ourselves, everyone asked us afterward, '**Who does Dragon change into?'***  

> *Right*

> ***And at one point we did have her change into a Pegasus, a biiig pink horsie with wings ... and I still think offscreen, she's a pegasus somewhere right now, wondering what the heck's going on and flying around...and then she changes back into a dragon before the end of the movie.*** 

And from the film's Second Audio Commentary (between Producer Aron Warner and editor Michael Andrews): 

> *Someone asked me "**what about the Dragon, how come you don't see her transform" and I said "funnily enough, we did do that at one point...but it was just a bit weird to suddenly jump back to the Dragon".***

> *Well **yeah, at one point the Dragon was a unicorn or a pegasus with wings.***

> *Yeah, she was part of the 'Rescue Team' later in the film but she looked too much like a pretty pony which was fine but it ended up just not hitting me...*


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As to why they didn't include her in the film until the very end, this is discussed in the film's second commentary. In short, it was because having a  **gigantic fire-breathing dragon** as an ally instantly destroys any sense of suspense in the fim

> *We tried to put her in, several times before but... but you can't have
> her around a lot because she, **'cause she gets everything done. She can
> get through any obstacle.***
> 
> *Like we couldn't have her to get into the castle or anything
> like that, or to get those guys out of prison. **It would have just made
> it all too easy.***


  [1]: http://scifi.stackexchange.com/a/73138/20774
  [2]: http://bluray.highdefdigest.com/4164/shrek_whole_story.html