Talk:My Little Pony Equestria Girls: Friendship Games/@comment-10390252-20150829194516/@comment-26940653-20150829203552

That's also what I've been thinking: Pleasant emotions with pleasant actions to go with them (as in, doing something they enjoy). There's probably other triggers of their transformations — for example, playing together as a band, and as such being in harmony as a group.

It'll probably be elaborated more in the film. Who knows, maybe it even works as an "emergency transformation" to inmediate danger.