Well this can go into some “interesting” places

@KuroNeko
 
@thps48  
Seems like I am not the only one who is trying to put some kind of logic in to this.. :D

@AlexAngel  
Pharynx showed us that it’s possible for changelings to turn into things bigger than they are also, according to the guardians of harmony comic, Changelings can’t turn into something as big as an adult dragon (I don’t know if this rule applies in the show).
 
I think that, although they can rearange their body, they can’t create matter and if they try to take a form too big for them, their body will lose its cohesion an fall apart, meeting the same fate as a demon who is summoned improperly in the shin megami tensei serie.
 
Also I like the idea of these two loving each other in spite of the huge size difference.

@AlexAngel  
Pharynx is presumably more skilled at size displacement. In fact, I’d imagine all changelings can become objects smaller far more easily than objects larger. Though, we don’t completely know what qualifies as strenuous usages of changeling magic outside of alicorn transformations. :3

This makes me wonder how big Thorax can become as a dragon, and how much mass he would have. Sigh… I am overthinking this.

YES!!! There is truly not enough of this ship thank you.