I'm not exactly sure who to credit for the next Avacyn Restored spoiler. The img file was titled "svmnomdam - preview." But your best bet is to Google the words in the watermark if you want to track the original source:
Nice. I'm not sure how nice yet, but Misthollow Griffin is unique among all magic cards and that's good enough for me. Four mana for a 3/3 flier may be good enough for limited (although even that's a little suspect in a triple Avacyn Restored draft format where it seems like half the creatures are going to have flying), but at that price, it's not going to fly in constructed unless it's unique ability is seriously abused. And I wouldn't have it any other way.
This is basically my dream card. It's costed high enough so it's not busted, but it's unique enough to only fit into an equally unique deck... which brings us to an old favorite of mine that's been looking for an update.
For Misthollow Griffin, I'm going straight into my archives and digging out my Twenty Cards or Fewer deck. I could even start from scratch if need be, but Mistollow Griffin wants to be exiled and what more efficient way to exile it than Serum Powder. With the powder, you're essentially have the potential of mulliganing into an 8, 9, 10, or 11 card hand, depending on how many griffins you hit. Throw in other cards like Desperate Research and Arc-Slogger and you have multiple ways of removing the griffin and getting maximum value.
I'll have to revise that deck later, but I like it.