Hearthpwn

I have never written a mulligan guide, but I will try to do it now and to be the most accurate possible. I will break down each single matchup, with and without coin. In general, the most important cards to search for at mulligan vs. pretty much everything are a 1 drop and the Razormane.

VS. DEMON HUNTER
The most popular DH decks right now are the Quest/Brute and the Fel/Jace: the former is quite a favorable one unless they do things like double Brute on turn 4. The latter I think is the worst matchup for us alongside with Quest Shaman. However, the mulligan is the same, let's see why.
In both cases, having or not the coin isn't relevant for the mulligan strategy since they aren't going to develop any threatening board in the first couple of turns. The Quest/Brute variant can play the 1/1 or the 1/3, and the Fel/Jace variant could play a Mo'arg, but nothing more than this, so they don't affect what we are going to search for in the mulligan. 
In both cases, their HP costs 1 so we are not going to keep 1-drops with 1 health, basically all of them except for Sow the Soil, that must be kept. 
In both cases, Composting is so important, either for trading our board into the Brute or to recover from an AoE.
In both cases, Cultist is a must keep cause it blocks big draw turns or removal turns. 
So, alongside with the Razormane, we are going to search/keep: Sow the Soil, Composting, Cultist, and Augmerchant only if we already have a minion with at least 2 health.
NOTE: against the Quest/Brute variant Oracle is devastating, but we are not going to keep it since it's always better to assume that we are facing the worst matchup. 

VS. DRUID
First of all, it must be acknowledged that the matchup against slow spell Druids like Anacondra and Celestial is basically a free win, because the board we build is uncontestable for them except for Celestial which can use the C'Thun AoE spell, but we can easily recover from that.
Therefore, we are always going to mulligan for the mirror, in which we should have a slight advantage thanks to the Kodo (90% of lists don't run it) that can swing the board in our favor in mid-game. 
The most important cards here are Razormane, Panther and the Mount Kodo. However, the 4-drops are never a keep in any matchup, but it's important to draw them later in the mirror to shut down their board. Razormane instead can be game deciding if one player sees it and the other doesn't, so we must mulligan hard in order to find it.
Without coin: always keep the Razormane and at least one 1-drop, if you have multiple ones keep the best one (my personal ranking in this matchup is: Peasant, Sow the Soil, Squirrel, Augmerchant), otherwise toss everything to search hard for the Razormane. 
With coin: keep Razormane, and toss everything, even 1-drops, to seach hard for the Razormane, because it can be coined on turn one.
In both cases: keep Augmerchant if Razormane is already in hand.

VS. HUNTER
Here we win by snowballing the board early. In order to do so, we must prioritize any 2-drop instead of just the Razormane, because if we toss a 2-drop to search for the Razormane, we risk to draw other cards that aren't a 2-drop. 2-drops are so important because of the things Hunter can use to contest our 1-drops that have 1 health, namely Crescent, Wolpertinger, Wound Prey. Also, most of them are taunts with good statlines, that can both do value trades and prevent the Hunter's damage going to our face. Cultist is also very good because it slows down Rexxar's cheap spells.
Without coin: keep at least one 1-drop (Sow the Soil has the priority) and any 2-drops, Oracle if we already have a 2-drop, and keep Augmerchant if Sow the Soil and a 2-drop are already in hand;
With coin: keep Sow the Soil, any 2-drop, always Oracle, and the Augmerchant if we have wither Sow the Soil or a 2-drop. 

VS. MAGE
Apart from Razormane, priority here goes to Composting for recovering after the opponent's removals, and to Cultist for avoiding AoEs. We win through constant pressure, especially thanks to our 4 and 5 cost cards.
Without coin: keep at least any 1-drop, Razormane, Composting, Cultist, and Augmerchant if Sow the Soil, Razormane or Cutist are already in hand.
With coin: same as without coin, unless toss 1-drops that have 1 health, and keep Oracle.

VS. PALADIN
Same rules as against Hunter. 

VS. PRIEST
Same rules as against Hunter and Paladin. 

VS. ROGUE
Here we keep everything playable in the first couple of turns. We must pressure them in every way possible. If they answer us, gg, they eventually reach their Garrote win condition (I'm speaking of Miracle Garrote Rogue, the Poison variant is a free win). If they don't, we win. Only exception is that if we have coin, we toss 1-drops with 1 health since they get contested by HP.

VS. SHAMAN
Same rules as against Mage.

VS. WARLOCK
Same rules as against Mage and Shaman.

VS. WARRIOR
Haven't faced a single Warrior with this deck, can't give any tip unfortunately.

Hope this can be helpful. If anything's missing or not detailed enough, please let me know so that we can discuss it.

Updates on the deck's performance: currently 43-18 (70% winrate), still in top100. Proof: https://imgur.com/gallery/6BL8q25

Hi, sure! 2nd Teacher's Pet will do just fine: even if it hasn't the same power level, it's still a good card that can be cheated out on turn 3. 

You could also try Traveling Merchant, a card that I would like so much to test cause to me it makes a lot sense here, it fills the 3 mana slot which is kinda empty and it synergizes with the wide boards we build. 

Please let me know your choice in the end, and if it's the Merchant, maybe tell me something about it :)

Doing great with this deck so far! I'm at a 57% WR at Diamond 4 right now. I replaced Greybough with Mankrik. Thanks for posting. 

*edit* I didn't have Greybough at the time of posting this, but I do now and he works much better than Mankrik! :)

magniffecent deck! Without any practice navigating through diamond 6-3…. Greybough is an mvp, I would-be not change him for mankrik, card draw is the weak spot…

I've been having really good success with the deck! So far I'm 10-1 from (Silver to Plat w/ Diamond 5 MMR) having subbed in another Teacher's Pet for Greybough because I didn't want to invest the dust just yet, but honestly I might, since I think this has been the strongest deck for me the entire expansion! 

Any chance you could do a mulligan guide? I've been referring to the HSReplay list but it's slightly different, and having explanations for certain mulligans would be super helpful. 

Either way, thank you bro!

Alright, so after more testing I've come around to your point of view. The cults are very strong, and overall curve feels good.

However, I like to tinker with decks... so I thought about your question of what could be cut... and most things on the list feel pretty good. To me, the weakest cards are the 5-drop taunts, which are great on curve with Razor or with the Oracle combo... but otherwise are pretty slow (and graybough really would be better in a different meta).

So, i've tried an experiment of replacing them with Ogremancers, which seems very anti-synergystic at first, but hear me out! the Ogres are strong vs Shaman, Mage, DH, Warlock and even Hunter, and there's actually a lot of good synergy because they create an extremely wide board for composting/arbor/sow the soil. They may be less good vs more board based decks which are a) less popular and b) pretty good matchups already.

Anyway, it's a relativly small sample size, but seem promising so far. Either way, they take a lot of resources for a spell deck to deal with and won me a few games so far vs shaman (which makes them already worth it in my mind). It may be that they end up being less overall synergystic in the end (again, you give up a few high-rolls), but I'm optimistic so far.

Hello!

Can we replace Greybough with something else? Missing him right now.

Sure, what you're saying is true, but you're missing out on the other upsides. For example, vs control you often want to hold some cards for a big value play with oracle or composting - blooms provide a lot more ability to do that. Are they the best for the deck? Idk cause I don't use data, but I can tell you that in playing they feel really good. I'd try them out!

Mage and shaman got so many good AOE spells this deck gets demolished pretty quickly and by turn 6-7 they always complete the quest and your face explodes to burn damage(while having absolutely no board because it gets demolished by spells every turn)

HS went to total shit this days... oh yea and there's still quest warlock but he at least rarely survives due to lack of proper AOE in standard

this deck is the bomb m8 well done currently 90% winrate from gold to d4 still going strong

After a little testing I still like the blooms (allows crazy things like a turn 1 panther, etc), but think the annoy-o/brawler/mule package is better than with the toads. I would try subbing cults for blooms and seeing what you think!

Been running an almost identical list except with toads and blooms over brawlers and cults. I'll give this one a shot! The blooms are definitely hard to judge, win some games early on with them, but they're basically a dead draw after turn 5. I like that you're doing the Kondos and Panthers too, that's something I switched to a while back with great success.