The Scarab God - $9.99
Everyone I've talked to about The Scarab God seems to think that it's either totally nuts or completely unplayable, but the truth is probably somewhere in the middle. If Zombies wants to move into blue and give up a little bit of aggression for a lot of inevitability, The Scarab God seems great. Outside of that deck, I'm not feeling it. Either you've got a lot of Zombies and The Scarab God is killing your opponent quickly or you don't have a lot of Zombies and you should probably be playing something else. Zombies is a solid deck, though, and The Scarab God could end up at $15 if it's a four-of staple in the newest iteration of that archetype. This is too narrow a card for me to speculate on, though, so I'll be staying away.
Razaketh, the Foulblooded - $7.99
Razaketh, the Foulblooded isn't powerful enough to be a Modern ramp or reanimation target, but it certainly could take on one of those roles in Standard. Its ability plays really nicely with Cryptolith Rite, so it could very well end up as a curve-topper in that deck. Somewhat ironically, it plays pretty well with Liliana, Death's Majesty too.
I can certainly envision a world where Razaketh, the Foulblooded ends up at $15-$18 because one of those decks ends up being the best in Standard. It's unlikely, though, and casual play probably can't sustain a price tag above $4-$5. Feel free to buy in if you feel like you've unlocked a new top strategy, but that's not how I like to roll.
Uncage the Menagerie - $5.99
Those of us who love Uncage the Menagerie might be overrating it a tad because it looks like a lot of other excellent spells. I've heard Chord of Calling, Green Sun's Zenith, and Collected Company comparisons being bandied about as comparisons, but Uncage the Menagerie doesn't have a ton in common with those cards. Tutoring for a creature and placing it in your hand is significantly worse than getting something that can hit the battlefield immediately.
That said, I do think that Uncage the Menagerie will be played in Standard. Most decks have a couple of different two-drop and three-drop creatures regardless, and a flexible spell that reads "3GG: Draw three creatures" seems fine. If someone comes up with a way for it to fetch an entire two- or three-card combo in Modern, it could even end up as a format staple in some fun new archetype or a slightly remixed version of Abzan or G/W. $6 is a reasonable gamble to take if you're higher on this card than I am, because these are the exact kinds of effects that end up being broken and expensive. And honestly, the multi-format upside of Uncage the Menagerie is far higher than either of the other mythics we've discussed so far today. I still bet it'll end up in the $3-$5 range, but I'll be monitoring this spell closely.
Nimble Obstructionist - $4.99
Nimble Obstructionist is an excellent and versatile card. It would probably be somewhat playable even if the cycling text was all it had, but the flying body with flash is a great way for U/W tempo strategies to take down problematic planeswalkers. I know it's been a few months since a deck like this was good, but U/W has been a Tier 1 strategy many, many times in recent history. Expect this card to stay in the $5-$7 range and buy in accordingly.
Rhonas's Last Stand - $2.99
Now here is a card that's either absurd or unplayable. Double green is tough, but there are times when this will come out on turn 2 and win you the game. Of course, there are loads of other times when it immediately dies and you are unable to ever regain the tempo advantage that you just lost.
I have a hard time pooh-poohing a card that is so close to Tarmogoyf, and I'm going to look really bad if Rhonas's Last Stand ends up being absurd, but I just don't see it. Aggro decks just cannot afford to either skip turn 3 or play a two-drop that isn't good to cast during the early-game. At that point, why not just play Longtusk Cub? If Rhonas's Last Stand hits, I think it'll be as an early blocker in something much slower, but that's where the double-green comes back to hurt you. There's a small chance that this is one of the two or three most important cards in the set, but I suspect it'll be a future bulk rare instead.
Earthshaker Khenra - $1.99
Earthshaker Khenra feels like a solid four-of in a fast Mono-Red or R/W shell and a blank in most other competitive brews. If Mono-Red ends up making a comeback, this could spike to $3-$4 for a bit. If not, it'll end up in the $0.50 to $1 range. If you've already pre-ordered your playset of these and are waiting to sleeve up the next iteration of your Mono-Red brew, great. If not, don't worry too much about Earthshaker Khenra.
Torment of Hailfire - $1.99
Punisher cards tend to be overrated during the preview period because their upside is easy to see. What's more difficult to project is how good Torment of Hailfire will really play during a heated match. Remember: if you're not pressuring your opponent's life total, this will just deal nine to twelve damage and then you'll die. If your opponent has a bunch of extra tokens or whatever, they'll sacrifice them and then you'll die. If they have a lot of cards in their hand and battlefield advantage, they'll discard them and then you'll die.
I don't think that Torment of Hailfire is unplayable, though—this is a lot of scalable raw power to have under your control. I just think that its utility is limited to grindy, midrange matches where all three modes are solid. This is a "see how the pros are reacting and act accordingly" track-and-follow for me.
Hostile Desert - $1.99
Hostile Desert is too good not to see play somewhere. It's got some potential in Modern alongside that format's full slate of fetchlands, but most of those decks have high color requirements already: the reason why Creeping Tar Pit is good is because it fixes your mana and it attacks. Hostile Desert is actively bad at its most important task, though the fact that it doesn't enter the battlefield tapped is a nice bonus. Eldrazi decks might want this, and I still think that there could be a "Deserts matter" deck somewhere in Standard, but I doubt it'll be ubiquitous. At just $2, though, it doesn't have to be. A Modern-playable land at that price? I'll grab a set now just in case.
Djeru, With Eyes Open - $0.99
At five mana, I doubt even a new take on Superfriends would have much interest in Djeru, With Eyes Open. Why not just put another top-tier planeswalker in your deck and cast that instead? It's got some marginal utility in Commander, but not enough to keep it from being a future bulk rare.