There had been a series of tests a few years earlier. Quietly conducted by Twilight (of course), she had sought to find out where the limits of changeling magic were. And after quite a few trials, the results were clear: a changeling could assume nearly any form, but those forms were only physical. A changeling in the shape of Princess Celestia couldn't move the sun; one in Starlight Glimmer's couldn't execute obscenely powerful spells; one that looked like Fluttershy couldn't talk to animals; and one that pretended to be Rainbow Dash couldn't do a rainboom. 