Koolkoal: All the Bulbasaur's line doesn't seem to fit very well both in the color pie and with the card themselves. The effect of the first two belongs to blue, while all the pinging seems more something a red card would do, since green tends to "fight" other creatures, with some exceptions with flying creatures and old cards. Charmander is a classic dragon, but I like the way it evolves. At last, I don't like that Squirtle's line is just a bad, uninspired version of Charmender's. It doesn't even get the cools keyword abilities the others have!
NinjaCaterpie: Oh, the Shapeshifter of equipments! I think that these three cards could stay together on a single face with some smart wording and costing. I like the versatility of the card overall, but I'd leave monstrous rotating prisms for something more complex.
Megiddo: I like that the outer faces unlock the inner face: it feels like something mystic. In limited, the epiphany will probably never come, but I like that it still is a solid card due to its versatility. Since the work you have to do to finally cast the Sphinx, I wouldn't be so shy in making it a 4/4 for 2UU, even if the value is already high when it hits the battlefield: I wouldn't be surprised if this could be even a 5/5 in a hypothetic real print, to make it an efficient finisher.
Ulka: Oh, a return to the original DFCs! I like that there's no way back from the ultimate form from a flavour perspective, but I really think that Kvistur wants to do too much. I don't bother the pumping effect, but a single sided Wheel of Fortune plus being virtually free might overwhelm your opponents. I'm not really a fan of the drain effect of the Terror too, that makes me think of black more than the gruul colors.
With some fine tuning, this could be a really cute, ehrm, triple faced card.
Mergatroid_Jones: Wait, where is my PRISM. Of course, this would be a really cute way to hit nostalgia in an un-set. Like the idea, like the chosen cards (Blastoderm? crazy.), like less the "laziness" as a CF entry!
Sporegorger_Dragon: Woah, woah, woah! We've gone full Ugin here! Two things that stick out immediately to me: the first, 'Ugin, the Ascendant' is incredibly packed with text and it would hardly fit in a normal card face so, unless the unfolded part is some kind of scroll, you should probably do a word count check. The second, is that when you have the Newly Sparked, you probably don't really bother to upgrade it once again, since it's already incredibly strong (ultimate after one turn, while creating 2/2 for defending himself?). I mean, you are probably fine with the 4/4 flying dragon that comes down on turn two/three already!
Overall, in my opinion, a triple faced card that wants to be too sensational.
Cythare: a very cute idea that could probably be printed as a double faced card too, with the aid of a custom frame (on each side, one of the instant modes combined with the relative creature). I like that this preserved some of the original Warewolves' flavour and that this can be exploited both by you and your opponent. The Mage-Eater is a relentless hate card and the only flaw that I can see, is that it's a bit too efficient: you counter their spell and get a 3/3 that continuosly grows and deals heavy damage to it. If they want to deal with it by using its "weakness", they need to cast two spells and pay 4 life for it, and then watch your counterspell getting back in your hand! The Beta is a fine, more balanced, card.