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Neutral
Potion Vendor: Hey, a good healing card for those Druid healing synergies! And maybe for Priest Northshire nonsense. Much nicer to have this battlecry on a smaller minion than on the 3/3 for 3 it was previously on I think, especially for Priest Northshire shenanigans, might push this into seeing more play than that did.
Toxfin: If Murlocs are good, this is too. As with every time they've printed more Murloc stuff, I'm just crossing my fingers that the resulting deck isn't good.
Arcane Servant: River Crockolisk but an elemental. Even Elemental decks wouldn't run this. Filler.
Dalaran Librarian: Neat, but the only deck I can imagine wanting it is Silence Priest, and I don't think that looks good enough at this point.
Mana Resevoir: 2 mana, 0 attack, effect is just spell damage. Crap. Plus we saw this as a 3 mana demon with just +1 health before, and that saw no play, so yeah, definitely crap.
Spellbook Binder: Eh, I doubt there's enough good spell damage cards or decks that want them to get this guy into constructed.
Sunreaver Spy: Very strong secret synergy card, basically custom-made for Paladin, since they're the ones who can curve it out. Pretty good evidence that Secret Paladin will be a real thing.
Arcane Watcher: Interesting that they let it attack if you have any spell damage, but spell damage cards generally aren't good enough to make that worth it, I think. Silence Priest might run it, if that works, but I'm inclined to think it won't.
Faceless Rager: Might actually see play, honestly. A Handlock-like deck could get a lot of use out of something like this copying the high health of a Twilight Drake or Giant. Needs a specific deck like that which can get good, durable minions down early though, I think.
Flight Master: Weird, probably bad.
Hench-Clan Sneak: Mediocrity incarnate. Arena card, nothing more.
Magic Carpet: Probably not good, but maybe somebody comes up with a deck that can abuse it somehow. I'd bet against it though.
Portal Keeper: Probably not good, except that it does have great synergy with Plot Twist. If it sees play, I'd predict it's in exactly a Plot Twist-running Warlock deck.
Proud Defender: Very nice taunt minion, the closest thing we got to a replacement for Tar Creeper. Probably not as good as that card, but I think there's every chance this guy sees a lot of play in Control decks.
Soldier of Fortune: The drawback is probably too much for this to see play.
Violet Spellsword: This might be playable, it becomes decent at 2 spells in your hand, above-average at 3+. You're probably really gunning to consistently have 4+ though to make it strong, and that seems iffy to me.
Azerite Elemental: So its stats aren't good, and its effect is just spell damage, that doesn't even happen unless it survives a turn. Yeah, this looks pretty bad.
Dalaran Crusader: Pack filler/arena card.
Recurring Villain: Actually has potential, I'm just not sure what decks have enough buffs to justify running him. He does only need +1 attack to trigger though, so maybe Druid with their +1/+1 AoE effects? Seems a bit costly for Token Druid though.
Sunreaver Warmage: Interesting. If Big Spell Mage were still a thing, this would have an obvious home there, but all of those cards are gone, so it's a theoretically good card in search of a deck that runs enough big spells for it to work. May or may not find it, I'm not sure right now.
Eccentric Scribe: Not bad, but probably not constructed-worthy.
Mad Summoner: Very strange card. Goes great with the new Warlock AoE/buff spell, but I think that may be too specific a combo to see play, and I struggle to think of what else you would do with it.
Portal Overfiend: See Portal Keeper comments.
Safeguard: Seemed to have potential at first glance, but upon reflection, it's basically worse Rotten Applebaum - +1 mana to turn the healing into a 0/5 taunt. Maybe Deathrattle Hunter sees enough value to having it around for Oblivitron that it runs it, but I'm skeptical even of that.
Violet Warden: One of the better-statted spell damage minions we've ever seen, actually. Still probably falls short of seeing constructed play though.
Underbelly Ooze: It's Grim Patron, but 2 health bigger and 2 mana more. Hard to completely discount it given that card's history, but the higher mana cost makes it harder to work with. We'll see if somebody finds a way to break it.
Tunnel Blaster: That's not bad at all, actually. Reminds me of Primordial Drake, though the AoE being a deathrattle instead of a battlecry is definitely worse. Might still be playable though, especially if aggro is a concern.
Heroic Innkeeper: Bigger Frostwolf Warlord is worse Frostwolf Warlord. Crap in constructed, but very good in that "all minions are 1/1 and cost 1" Brawl.
Whirlwind Tempest: How many good windfury cards are there again? Oh, hardly any? And it's 8 mana, so you're not comboing it with anything ever? Yeah, this sucks.
Burly Shovelfist: One of the better high-cost commons we've seen, may even verge on having a use in constructed (Rush Warrior?). I'd still lean against it, but there might be the off chance.
Druid
Blessing of the Ancients: On the one hand, this is +2 mana over Mark of the Lotus. On the other, Twinspell. May well enable Token Druid once again.
Hunter
Rapid Fire: Good card that probably goes in all Hunter decks. It's 4 "ping" cards for the price of 2, which is solid enough on its own, and could get scary with Vereesa Windrunner. A swing with her weapon sudden turns these into 4 mana deal 12 (plus the 2 from the weapon). One of the better Twinspell cards, I think.
Ursatron: Solid card that almost surely goes into Deathrattle Hunter.
Arcane Fletcher: Interesting. Very specific both in its trigger and what it draws you though - feels like it wants to be in a combo deck of some kind, but I don't know what that deck would be.
Hunting Party: Probably too slow to see constructed play.
Mage
Magic Dart Frog: Flamewaker Lite is probably still good enough for Tempo Mage to run it. Would definitely be if it still shot twice per spell, once is definitely notably weaker than Flamewaker, but I'm still inclined to think it's enough to see play in that deck, if that deck works out at all.
Kirin Tor Tricaster: I am not sure whether this sees play or not. It's mainly strong with Arcane Missiles and Shooting Star, but its drawback can be mitigated by Sorcerer's Apprentice. But it's also competing with the 4/3 spell damage +2 card, so unless you run both, that probably just beats it, I think.
Paladin
Mysterious Blade: I was actually watching the reveal stream, and let out an "F you" at the dev who remarked about how a 3/2 weapon would be too good to print without a conditional. Anyway though, yeah, Firey War Axe is back, but in Paladin for some godforsaken reason, and it needs secrets to work now. But secret on 1 into this on 2 is strong, so yeah, Secret Paladin will probably be a thing. I just hope it turns out more midrangey rather than aggro, so I might actually play it.
Priest
Hench-Clan Shadequill: For +2 health on Yeti you're getting Zombie Chow's drawback? Eh, much as Priest doesn't generally care about that, I'm still not sure that's worth it.
Unsleeping Soul: We are back on pushing Silence Priest I see. Not particularly impressed by this one at the moment, I don't think it sees play, but if I'm underestimating that deck maybe it does.
Convincing Infiltrator: Oh hey, a strong deathrattle for that 2-drop from earlier to copy! I don't think this alone will make that card playable, but this one just might be. Not totally sure, but the potential is there I think.
Rogue
Daring Escape: Eh, probably doesn't see play. Rogue has better ways to return minions to their hand already, is generally happy just returning one, and there's no extra upside here beyond returning multiple.
Waggle Pick: One of the most solid weapon cards Rogue has ever been given. Likely to see play I think, it's just generally pretty good.
Shaman
Mutate: Eh, if Unstable Evolution wasn't seeing play outside of meme decks, I doubt this will either. Mostly exists for Hagatha's hero power to hand you.
Soul of the Murloc: Half-cost Soul of the Forest is frightening. Probably strong enough to go into any more aggressive Shaman that comes into being for the next two years, definitely in any Murloc Shaman if that works out.
Underbelly Angler: Frighteningly good, giving a Murloc deck much more staying power over the course of a game. This is the card that makes me worry Murloc Shaman will be a thing.
Witch's Brew: Why isn't this echo? Is it limited to just repeating once, maybe? Odd if so. Probably a card that mostly exists for Hagatha, I think, unless Control Shaman really desperately needs healing.
Scargill: Could be scary in the late-game, but since Murloc decks prefer not to get there, I'm not totally sure they'll want this guy, even if Murloc Shaman takes off.
Warlock
Impferno: Has potential in Demon Zoo, for sure. Not totally sure it makes the cut, or if Zoo wants to run enough demons for it, but will be tried.
Darkest Hour: I guess the idea for this is that you run it to combo with Rafaam's Scheme? That's about the only potential I see to it, and that doesn't look strong enough for me to think it'll see play.
Jumbo Imp: The "while this is in your hand" text kills it I think.
Warrior
Sweeping Strikes: Minions with this effect have never seen play, doubt this spell will either.
Vicious Scraphound: My favorite card from this last batch of reveals, goes in Control Warrior no questions asked. Great little anti-aggro card, great synergy with Zilliax, good to get off Omega Assembly and Boom's hero power, just all-around solid for a control deck.