When Moonform enters the battlefield, it becomes an Aura with enchant creature. Manifest the top card of your library and attached Moonform to it. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
Enchanted creature has flying and lifelink.
This is solid. You run the risk of potentially losing a better card than a 2/2 flier with lifelink, especially in base white where removal is scarce. However, Sultai has never had a problem with potentially losing a bomb to their shenanigans. If they can mill three at a time with no fear, you can mill 1 to get a creature that is very good in limited that could potentially have a better creature under it. You play this. I wouldn't be surprised if we see its average pick order creep up the more it gets played. I'll stop now - no one cares what I think about Limited playability unless I can identify the next Stoke the Flames, which this isn't.
Dromoka the Eternal
Legendary Creature - Dragon
Whenever a Dragon you control attacks, Bolster 2. (Choose a creature with the least toughness among creatures you control and put two +1/+1 counters on it.)
This is as good in EDH as it is narrow. Unfortunately for Dromoka, it's in the worst possible colors for a dragon that gets a benefit from lots of dragons attacking. Scion of the Ur Dragon decks can use this and likely will, and its being a dragon will bolster its price longterm. I'm just not super bullish about its Standard playability, even though it's just fine if it's your only dragon. This is obviously nutty in Limited, and I may try it out in Mayael, but this seems like most of the upward pressure on its price will come from it being a dragon rather than playability. Who knows? It's hard to say there won't be 5 other sweet G/W dragons in the set.
4 mana a turn or green direct damage? This is perhaps the best of the Siege cards so far, and they are all good. The second ability is however hard to trigger and likely gets you one or two activations in limited, but the first one is some sick ramp action. You're unlikely to be able to use the two mana twice a turn all the time, which is what makes this card so fair and may make this one of the worst sieges in limited, but if you can either use or bank the mana in other formats, I can see this taking off. EDH has a million ways to use two mana twice a turn so this will be very useful. I don't know if this can ever go over a few bucks, and hype may put its presale price out of reach, but I think this card has serious potential. That said, this is just another card I have to give the "I love this card and I wouldn't touch it with a ten foot pole until March" rating.
Silumgar, Dragon Usurper
Whenever a dragon you control attacks, defending creatures get -1/-1 until the end of the turn.
Anyone with a Sion of the Ur-Dragon deck is salivating right now with all the sweet dragons we're getting that trigger when other dragons do stuff. This is going to help in combat by essentially boosting your non-flying blocked creatures and if you swing with enough dragons, they may not be able to block at all. I think this is probably OK, but I think it's in the same boat Dromoka is in. I imagine I won't like this at whatever its presale price is likely to be.
Wandering Champion, Marang River Prowler, Battle Brawler, Hungering Yeti, Abzan Kin-Guard
This seems like a pretty sweet cycle. I don't think these will matter financially, unfortunately, but they are all pretty sweet. I think they are less playable than Flinthoof Boar cycle if we're talking constructed, though.