The next blue uncommon for Avacyn Restored is spoiled:
Nephalia Smuggler is a decent card on its own which suddenly turns great when he's in a set that features undying, soulbone, and other "enters the battlefield" effects. He can give your undying creatures infinite lives, he can rebind unpaired creatures, and everything suddenly becomes increasingly unfun for your opponent. (And you thought undying was obnoxious in Dark Ascension? Think again.)
There are a number of decks that could use Nephalia Smuggler to help abuse a number of combos, almost too many decks to count. But... it's a shame the smuggler is a "human rogue" and not a wizard or cleric. He's exactly the type of 1 drop my Cube wants to feature and yet... it's not going to make the cut. What a shame.
Other than that, if you wanted to get creative, I think you start with cards like Threaten. Unlike Flicker, when the creature comes back into play, it comes back "under your control." Meaning that if a creature left play temporarily under your control, it then comes back permanents under your control. You could even go Grixis and start thinking about cards like Olivia Volderan. Like I said, the possibilities are endless.