Isn't Feast a card that upgrades itself?
I think I'm intrigued by this "cards that upgrade themselves" idea the most (well, next to Shelters). I had thought of the idea of a card that changes when you play it, but I hadn't gotten anywhere with it.
I have to say, though, I'm astonished at the themes for this set, particularly since they're for such a large set. I'd never have thought there was enough juice in the upgrading idea to be a theme to a whole set, because I can't imagine how many ways you can upgrade cards that we don't already have.
Similarly, as one who has preached against "retrieve from the trash" fan cards, I'm astonished that the trash will suddenly matter now. Of course, nothing says we'll get "retrieve from the trash." And if we do, I'm sure it'll be done in a very careful and clever way that circumvents the much-discussed problems. Actually, if we're about to get a couple dozen trashing/upgrading cards, it'll severely reduce the main problem, which is that cards in the trash are trash. Just the same, I think it more likely the trash theme cards would be things like Treasures and Victory Cards whose value varies depending on what's in the trash.
Super excited now.