I’ve been noting down my experience with, and strategy for, the Hearthstone Adventure encounters each week on the EJ forum. I just realized there’s no reason not to put them here for people working on the fights now. I know they’re mostly over, but I’ll put in this week’s anyway, and maybe paste in the old ones sometime for people trying to do them later.
Descriptions of the bosses and their decks can be found here.
Razorgore: Probably lots of easy ways to do this. I went with typical Freeze Mage-ish board clears. His only value advantage over you is creating 4-5 HP worth of stuff to beat down every turn, which is not hard to overcome just by establishing board control in conventional ways. An early Doomsayer and a late Flamestrike help you lock it down though. He Corruptions big threats, so typical midrange creatures to own the board work great.
Vael: Lots of ways to deal with the fact that he aggressively mills you. I went with Rogue both for being able to spam out cheap cards right from the start (especially with Prep and Shadowstep), and being able to counter-mill him with Gang Up. In my game, he milled out ahead of me–I guess he must have burned one of his Gang Ups–which made it easy. If you ever get one good Blade Flurry off for a big reset, you should be fine. He doesn’t have a huge number of minions in his deck.
BGH is handy for Giant spam near the end, and can be good with Shadowstep or Gang Up. Other than that, you might not want much costing more than 2. He will Naturalize creatures, so be careful trying to set up a huge threat like a Van Cleef. But that can be great if you draw out the Naturalize (or see them burned). Also, be very careful about lethal range, since he has 0-cost burn he can spam at you.
Chromaggus: Really fun encounter. I think there’s a probably a great plan around using Warlock cards to discard from your hand, but I went with Priest. Chromaggus has no hard removal, so a huge Divine Spirit-Inner Fire combo can win uncontested. No matter what your deck, bias towards being very cheap again, since you have to spend a lot of mana clearing out his trash (the only exception for me was Thaurissan for obvious reasons). I bet Cho is amusing if you have him.
You have to put with some of his curses for a while, and know when to get rid of them. The initial Green will probably sit for a long time, so you have to first take control and then start damaging him. I tried to use Lightwardens to abuse his auto-heal every turn (and to worth with my own Lightwell which was very good here). You may have to live with the Red you get on turn 3 for a while also–you probably need to make a turn 3 play (especially since the turn 4 and 5 Blue/Bronze are really important to drop immediately). Getting some semblance of control in turns 1-2-3 is huge. You need some way of removing a growing Drakonid on your turn 3 (SW:P is good).
Bronze and Black should always go immediately (exception: consider leaving Bronze if you’re about to follow up with a good board clear). Blue is ideal to let go of early on, since he can spam out 0-cost Flamehearts–but you can leave it if he’s already played a bunch of spells from his hand. Drop Red when you can, and Green once you’re in control and ready to win.
Nefarian: Nothing about this fight seems to shout for one particular strategy–it’s mostly a normal Hearthstone game with him having a huge value advantage over you (starting at 9 mana/turn on turn 2, and getting 2 cards a turn).
You can probably use anything if you have a plan for the early game (just survive his 9-mana turns on your 3/4/5 mana turns), the mid game (probably need one really good board clear), and the late game (actually killing him and dealing with occasional damage). I used Paladin with Humility/Chow/Doomsayer/Aldor for the early turns, an Equality-Consecrate whenever things got bad, and Lay on Hands/Guardian to take over at the end. As with all the encounters where you’re overcoming a huge value disadvantage every turn, if you don’t have the typical good legendaries for that, a good endgame is to stick a Kel’Thuzad. Nefarian also has no hard removal, but he does have Flamestrikes and various direct damage.
The random card you get from Rag on turn 3 matters a lot. All you care about is living so the 6/6 Taunt seems best, especially if you can protect it for a bit and/or having him waste tempo removing it. Mind Control Tech is huge, and Emperor Cobra can trade way up. A Doomsayer can delay him a turn at worst. Anything to get to the Equality-Consecrate or whatever you’re using to turn the corner. Some luck with him doing comparatively weak things with his mana on turns 2-3-4 (such as using inefficient spells from your class) can also go a long way.