Now that you mention it, I really want to see the return of this spell from It Ain´t Easy Being Breezies...



I mean, think of it this way:

The Mane Six go to Yakyakistan, but it´s too cold up there for them, so Twilight uses a spell to turn them into Yaks so they can be there without problem. I mean, they kinda threw this possibility out the window already, but I´d be willing to accept that in both instances when a pony traveled there, it was unusually warm or something.

Or the Mane Six go to the Dragonlands, and Garble once again complains about ponies always beating him. Rainbow Dash, seeing an opportunity here, picks a fight with Garble and tricks him into saying that if the Mane Six weren´t ponies, Garble would beat them. Of course, Dash makes sure Twilight hears that, so she uses this spell on her friends to turn them into dragons and, of course, beat Garble in any dragon competition he challenges them to (I don´t need to see Garble as pony, though).



Also, I´m surprised Hasbro didn´t consider using this spell more often. I mean, they make the show to sell toys, so a spell like that is their best means of justifying a flood of new forms for our favourite characters.