The rest, well...
I have a theory. Ever see Pinkie Pie do her magic fourth wall stuff when she's not super extremely happy? Doesn't seem like she can do it. That's why she needs the smile counters. I figured if she was making people smile, they would be more hesitant to be hostile, Cranky Doodle aside. So there's the other part. I took away the Hexproof though, that'd be way too powerful.
Having trouble with coming up with Dash's colors, mostly. Her abilities are all blue, but I don't see her as being all blue. Mostly can't think of anything for her weather abilities to translate.
That said - I saw the Smile Counters requirement as more of a fourth-wall thing. Pinkie Pie looking at you, furiously, and going "No! I'm not going back into your hand while they all look soooo grumpy-wumpy!"
Edit: Also, I would say to make Dash colourless. And give her a few different abilities that use different colours.
One White-Blue, something weather related...
One Red tap ability.
And one... I dunno... Green?
But seriously? They brought out a version of Shroud that only applies to your opponent's spells or abilities? Man, I'm so glad I quit. It's like they don't even TRY to keep balance anymore.
Also, I edited something in about how I would do a Rainbow Dash card :P
---------- Post added 2012-12-06 at 07:35 PM ----------
I'm questing in Hyjal. I do the quest where you gotta save Goldrinn, the giant wolf guy.
I rode him back to town, then went AFK before I picked up the quest he offers.
When I came back to my computer, he had despawned and I can't pick up the quest. And it's impossible to make him spawn again, since I've already completed the quest that does that.
But yeah, on RD... that's why I suggest colourless. Colourless is the closest thing you can get to a rainbow in MTG unless you're running a 5-colour deck.
And no one does that shit anymore.
How about a colourless creature with a Blue-Green activated, and a Blue-White activated?
Really though, Rainbow Dash would be more about the power/toughness than actual activated abilities. She doesn't sit back and use skills or abilities, she just charges in and kicks things.
" I'll tell you the ultimate secret of magic. Any cunt could do it." - John Constantine