Before the EUCC, we had the APCC, which was the first event with the new set and introduced a new deck in the [Amaxi the Cruel] archetype. As it won the event, it was clear some people were going to play it in future events. This means people will be playing it, so even if you have no interest in playing it yourself, you still need to know how it plays out in a number of matchups. So we started testing it and we came across a huge issue: you pretty much couldn't ever win against blue Hunter, and given that this was going to be the most popular deck, this was not acceptable.
So when you have a problem like this, you have a number of options. Firstly, you can give up and try something else. Not all deck ideas will be competitive. There are plenty of other decks you could build and if your deck is getting crushed by everything, you can end up wasting a lot of time. Secondly you can accept the bad matchup if you beat everything else. It is pretty much impossible to beat everything and losing to unpopular decks is often fine. Of course, if I picked any of these options, this would be a very short article so clearly I'm going to go with the third option, which is to try and find something that helps with the matchup.
My first thought was just more early removal, like adding in [Drain Soul] and [Shadow Bolt]. While [Shadow Bolt] was fine, [Drain Soul] was pretty much useless as it often couldn't kill anything or required your [Sava'gin the Reckless] to hit. So if dealing with their early allies is needed, what else could we try? In this cased I moved on to [Sarmoth] and [Winter Veil Disguise Kit]. This is pretty much a hard lock against Hunters for which they don't have many answers. They need double [Concussive Barrage] or an in-play [Boomer] plus [Vanessa VanCleef]. Given that [Concussive Barrage] gets rowed a lot before they know what your plan is, and the other option often will take seven resources, you will win most of the games when you assemble this combo. This resulted in the matchup going to somewhere close to 50/50 which is a huge improvement and well worth the sacrifices you have to make in other matchups.
Hero: [Amaxi the Cruel]
4 [Cairne, Earthmother's Chosen]
4 [Sava'gin the Reckless]
1 [Lor'themar Theron, Regent Lord]
4 [Daedak the Graveborne]
3 [Fire and Brimstone]
3 [Summoning Portal]
2 [Soul Cleave]
4 [Boundless Hellfire]
4 [Banish Soul]
4 [life Tap]
3 [Miniature Voodoo Mask]
4 [Winter Veil Disguise Kit]
3 [Shadowfang Keep]
2 [Seeds of Their Demise]
This deck is pretty similar to the old list with a few changes. I've already gone over the [Sarmoth] + [Winter Veil Disguise Kit] combo, but you can use it against decks other than Hunter and [Winter Veil Disguise Kit] is fine on its own. You can just use it on [Sardok] then protect or keep any of your allies safe from attackers. The other card I've added is [Soul Cleave] which is very powerful with the token from [Cairne, Earthmother's Chosen] along with your other allies that don't mind dying. Other than that, this deck plays pretty close to how it did before, but in case you haven't played with this deck much, I'm going to go over how it runs.
As your plan against aggressive decks (especially blue Hunter) is [Sarmoth] plus [Winter Veil Disguise Kit], you need to mulligan for this. What you really want is [Winter Veil Disguise Kit] as you can [Summoning Portal] for [Sarmoth], increasing your chances you finding him. After you have set this up, you need to minimize the amount of time you are relying on it in case they break it up. This means using [Mazu'kon] to kill their allies even if they can't currently attack you. You also want to [Banish Soul] [Boomer] so they need to get to seven resources before they can cast [Boomer] and [Vanessa VanCleef] in the same turn. This will give you the time to remove their allies again so you don't just die if [Sarmoth] gets killed.
Against less aggressive decks you don't need this combo as much, so you can just row them. If they have effects that remove your allies from the game, you want try and leave [Shadowfang Keep] open rather than using it to play things out earlier so you can get their on-destruction triggers. You also want to be aware of how close to killing them you are. [Daedak the Graveborne] and [Boundless Hellfire] can deal a huge amount of damage suddenly, and this often means you can just attack their hero directly and force them to attack your allies. You also want to consider just flipping on turn 4 as it makes opposing [Mazu'kon]s and [Daedak the Graveborne]s much, much worse and weakens a number of other cards such as [Blood Parasite].
Overall, you need to be aware of what your game plan is in each matchup. Are you the aggressor or the defender? And then you need to mulligan and play accordingly. This can shift during a match but being aware of what position you start in is still very important.
Hopefully I've given you something to think about and if nothing else you can be aware of the potential that Warlock might have with [Sarmoth] plus [Winter Veil Disguise Kit] when you are playing against it. It is always good to know what other people might be playing if you have no interest in it yourself. You gain a different perspective on a matchup when you play from the other side. You learn what cards you are worried about and which don't bother you, so you can then use that info when you play against that type of deck.
You might even kind you really like this style of deck and it will give you more options on what to play in the future.