You can't at the moment no matter your strength or magic you'll probably have to wait until act 3 comes out which is why I'm assuming I can't figure out how to get pixie's last outfit but I'm sure it's doable right now unlike the Emma thing
Emma Cowgirl is basically a joke option. You're trying to get a mountain to ride you ;)
Pixie's last outfit: apply all the Hallowe'en decorations to your room (bed, jack o lantern and witch poster) and then sleep. Might take a couple of nights to trigger :)
