These new cards from Scholomance Academy were revealed today, including more dual-class cards and class legendaries!
Malygos, Aspect of Magic has proven to us that 8 health on turn 5 is hard to deal with. The persistent effect of Mozaki makes it a threat that must be dealt with though. We've seen fringe play with Small Spell Mage and can see this card adding a lot to that package. Combine it with Magic Trick and Ray of Frost, then use Evocation to grab some extra direct damage spells. Oh yeah, and it probably just slots in easily to Highlander Mage too, more realistically.
Just about any Demon Hunter card is likely to get our attention, as very few are eager to revisit the days of clear Tempo Demon Hunter dominance. Ace Hunter Kreen has an effect that summons some strong Kayn Sunfury vibes at first glance, allowing minions to trade into others without dying. Commanding Shout has not seen serious play outside of the old days of Patron Warrior, though, so this effect probably doesn't create much of a problem. The implications in Hunter are practically identical.
Priest fans are always game for taking resources from their opponent. Cabal Shadow Priest has always been a cornerstone of that strategy, but it may get dethroned by Cabal Acolyte. There are plenty of low-cost spells that Priest wants to run already, namely Renew and Apotheosis. The latter especially could be a devastating combo with a 4 mana 2/6 with Taunt. And at that point, stealing a minion is just pure bonus.