In the case of Vanellope, she reduces the Strength of all opposing characters by 1, for one turn, every time you play another Princess character
There is another promo version of Mickey Mouse, Brave Little Tailor, that is serialized and printed in gold foil art which is only given out to winners of the world championships
The Amber and Amethyst deck is probably the easiest to master, while the Ruby and Emerald deck is the trickiest of the three to understand, although its probably the most flexible and adaptable of the three decks
So, he may not bring something unique, but he's certainly not a bad card to have padding out your deck
It would rate around the middle of this list, if the cards weren't about to rotate out of Core constructed