I'm definitely still wanting to keep this deck cheap (regardless of the Pauper status), although I would imagine it can be moved that way if need be (but it would come at the cost of the biggest combo as both Bower Passage and Levitation are uncommons, so not much point there).
So there is a LOT to respond to, so I'll try to move things in an orderly fashion.
Geist Snatch could be good to stop creatures with reach, but realistically, there aren't many of those out there to begin with and most of them are green. To which point I could just soulbond deathtouch to whatever creature and swing until they have to block it, or just overwhelm them with all my "unblockable" creatures.
Gitaxian Probe and the other "pay two life rather than paying the mana cost" cards are marginal in my books. The most of them end up helping your opponent or could simply be paid for (unless you're dealing with a card of a color not in your deck). But for drawing cards, I'm pretty well covered with Tandem Lookout, Amass the Components, and Triumph of Ferocity. Further, given that this deck, perhaps more so than most others I run, is going to need you to continue pressing your advantage early in the game, the thought of giving up even two life to an opponent could be a problem as I'd then have to keep more back on defense.
You hit the nail on the head with Tower Geist and given the number of Levitations in the deck, I'd rather run Aether Adept over Misthollow Griffin. While it doesn't have the natural flying, the cheaper mana cost will help the flow of the deck, as, let's be honest, the only real reason to run either is to have the Unsummon.
Gryff Vanguard is a five-drop 3/2 flyer. I'll already be drawing cards as I said above and for that cost you could easily score an Air Elemental or another comparably large creature.
Soul Seizer could prove fun and I might look into that. But for that cost, Mind Control achieves the same goal, is the same legality, and guarantees the creature claiming effect.
Favorable Winds is a good idea and I've put two of them in the deck.
All good ideas though and I definitely appreciate the feedback. NullParameter, if you give it a go, let me know how it plays for you.
imsully, which decks were you curious for an update on? Some of the ones I've posted on here for ideas I haven't actually put together yet (although I will in the next month or two), but I can give you an update on the ones I do have finished.