We continue mulling through the newly released, complete Dark Ascension visual spoiler here with card number 90 of 158:
This card wants flash. Regardless, it's still a 2/1 flier for 3 mana and that's not bad. But because it doesn't have flash, this card is all about offense and less about defense. And if you just want a defensive card, Voiceless Spirit is a much better choice.
I don't see Niblis of the Mist being played outside of limited.
That being said, of all the color combinations out there for limited, green/white is an obvious choice to make sure your small beaters get in for more damage (especially with a well timed Travel Preparations). But I'm going to go out on a limb and say this might fit into a red/white deck. Traditionally, the red/white deck in Innistrad is one of the weaker color combinations. But slap Niblis of the Mist on top of Crossway Vampire and Nightbird's Clutches to help creatures like Bloodcrazed Neonate get in for damage, and that color combination might have just gotten a little boost.