Sometimes a few lines within a Hearthstone patch note can mean a lot. That's precisely the case with patch 15.2: "Cards that Discover from a random pool no longer apply a class bonus." (Blizzard — Source)
Introduced with the Journey to Un'Goro expansion, the Discover mechanic was just tweaked to increase the variety of cards from random Discover pools. In short: you'll get fewer class cards to choose from.
What's changing?
Previously, class cards were 'boosted': they were "four times more likely to be discovered" (Ben Brode — Source). Since this percentage is now balanced and that class cards have the same chance to appear than neutral ones, a lot of cards and combos revolving around the Discover mechanic were indirectly nerfed.
The Warrior Hidden Nerf
Let's be straight on this: the Control Warrior was hit pretty hard by the nerf hammer. A lot of cards often played within this archetype are playing around the Discover mechanic:
- Omega Assembly
- Dr. Boom, Mad Genius (one of its hero power)
- Frightened Flunky — notably because it allows to discover a Taunt minion, and Warrior probably has one of the best Taunt minion pool in the entire game.
Worth to be mentioned, the Archivist Elysiana is also losing a lot of its power. Often played within the Control Warrior archetype, this card had a serious tendency to discover Omega Devastator, Boom Reaver, or Sul'Thraze. It will still happen, but less — much less.
Wait... How could it be a buff?
Yeah, how could it be?
Well, let's be honest: while discovering more class cards might be an advantage for Warrior decks, it's not really what you're aiming at when playing others such as Rogue or Mage.
Think about the Zarog's Crown generated by the Heistbaron Togwaggle. Would you rather Discover two Ragnaros or two 2/2 Edwins? In the end, neutral minions — especially the legendary ones — often have better stats than class ones.
Myra Rotspring is also worth to be mentioned since the same rules apply to Deathrattle minions: neutral ones are often better than class ones.
Also, Power of Creation suddenly became more interesting to play with — you got the point now: Mage 6-cost minions are mostly bad compared to neutral ones from the same cost.
Other cards have been seriously impacted by this update: Blazing Invocation, Dark Possession, and Golden Scarab were actually nerfed.
Will this sole tweak be enough to shake the meta upside down? Is it enough to overthrow the Warrior Control from its throne? The question still remains...