Oh man I know about this! I did costume design for a school play where several characters did on-stage transforms. So, here, have an info dump. ^.^ I'm not one-hundred percent sure on what will work best for you, though, so you may have to do some experimenting.
Okay, for fast reveals/changes, use snaps, not velcro. Velcro is for putting things on quickly, snaps for taking it off quickly. Or, if you can, use magnets! Magnets are good for putting on/taking off costumes really quickly; that's what all the Broadway costumers are doing. If putting the costume on quickly isn't priority though, use snaps. They don't cost as much.
Look up some videos of Broadway transformations, like Cinderella or the Lady of the Lake from Spamalot. It's an easy way to familiarize yourself with quick changes and get an idea of what you want yours to look like. I'd recommend a spin transformation, it's usually the easiest with dresses in my experience. Practice it, though, you might find something else easier. With the ice dress, which will be underneath, having such a slim skirt I don't think you can do a flip change like the Lady of the Lake does, the coronation dress would be to bulky underneath?? But maybe if you just rip off the top and flip skirts it might work, not quite sure on that one.
Off the top of my head and with little/no reference on the dresses, I'd say put snaps down the back and both sleeves so it rips off easy. If you can, make like a T with the snaps so that the arm snaps/back snaps connect at the neck? That way you can just grab the front with both hands and tug. The cloak part can be snapped/velcroed or otherwise secured to the underside of the coronation dress so when that comes off, the cloak is freed.
If you're using a wig and are changing that as well I definitely recommend magnets. Sew some into the wigs and into your wig cap. You can rip one wig off and throw the other on and it (should) be perfect. That's the technique used in the Shrek musical for the ogre/human changes, since Fiona has to change super quick.
I hope that all that info helped >.< Sorry if it's a bit confusing! If you need clarification just let me know, I'll do my best. ^.^
EDIT: I just watched the video that ichigo_m posted and that Elsa did pretty much what I'm recommending, just tearing the dress off from the front. I still recommend a spin, though, I think it looks pretty. ^.^
We can take what we are and fight for more.
Last edited by Aliyev : 05-17-2014 at 11:24 PM.