We continue mulling through the newly released, complete Dark Ascension visual spoiler here with card number 91 of 158:
I kind of like the spirits of Dark Ascension so far. Hollowhenge Spirit, Niblis of the Mist, and now Niblis of the Urn are all kind of interesting. And then you have late game, build around bombs like Drogskol Reaver it looks like upgrading the spirit tribe was one of Wizards' top priorities in Dark Ascension compared to their weak presence in Innistrad. This is a good thing.
And so far, from what I can tell, if there is a "spirits sub-theme" its all about combat tricks and tough choices. It's less about direct interactions (direct damage, counter target spell, destroy target creature, etc.) and more about pseudo direct damage, pseudo combat tricks, and pseudo creature destruction. And as long as the spirit creatures are appropriately costed, I think this can be a decent theme for their tribe.
Just like Niblis of the Mist, I think Niblis of the Urn wants to be either in a green/white aggro deck or a red/white aggro deck. Both of the Niblis spirits help damage get through to your opponent. And being a 2cc 1/1 flier, I don't think you can go wrong with the Urn.