Hearthpwn

Yet another satisfied user!!! Couldn't expect such a positive feedback from the community, I'm so happy the deck is working for so many players :)

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.

So happy it's working for you too, keep it up! :)

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

Your findings seem totally on point! True, the weakest cards are the 5-mana taunts (as I've been playing more and more games I've realized this as well), and true, the Ogremancer could give us some considerable percentage against control, especially Shaman. I will absolutely try them! Thank you so much!

P.S. Yesterday I was also evaluating Travelling Merchants, what do you think about them? Maybe not better than Ogremancer, right?

P.P.S. One last thought: Ogremancers could be slow and way less useful than the taunts in board based matchups, especially vs. Aggro. Maybe 1 Ogre 1 taunt? If yes, which of the two? Greybough seems to carry too much value and annoyance for the opponent not to be preferred over Teacher's Pet...

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 :)

My apologies, you are right, I didn't consider those situations which honestly aren't rare.
So, it's not that obvious not running Blooms, but for my personal preference I would still not to and that's why: up to now, I didn't do bad against controls (actually the stats from bronze to legend show that I scored 8-6 against them, plus an additional 2-1 in top100) while winning quite consistently against the rest of the field (Hunter is the closest one), and Blooms could have come handy just in those situations in which I would have wanted to combo Oracle with Razormane and Greybough/Teacher's Pet, or with Composting as you mentioned. But still, I did fine even without them in these cases.
I also did fine without Blooms in other scenarios, which of course doesn't mean that I couldn't do better WITH them, but I'm still stuck on the belief that the Overload is too bad in a deck which wins pressuring the opponent on board turn by turn. 

However, I genuinely don't know whether Blooms are truly not worth or the opposite. What I've written is just my personal opinion and preference, since I don't have any experience or data on the cards themselves for an appropriate evaluation. I just know that this particular list of mine is winning a lot and I would like to continue to play it like this.
Maybe we could try and search for actual data on them, but what would be the term of paragon? I mean, Bloom instead of what? Neophytes seems pretty core to me (actually, also everything else).

Hi, thank you for your comment.

The matchups you have mentioned are easily the worst ones, especially Shaman. Good removals equals hard time for this deck, but it is not necessarily auto-loss since we have multiple ways to try to deal with them, starting from our own gameplay which should pay more attention to resource consumption/hand size not to fall to too much behind if and when our board gets cleared. Options like holding to a Oracle+Composting combo, playing Arbor Up on an empty board, or Composting just a couple of minions might be useful in this regard. Other than this, we have 2 natural divine shields and 2 applyiable divine shields for more stickyness, Greybough which also sticks, 2 kodo's which give more resilience to our board (that if gets wiped, we are still left with a 4/2), and the Squirrels that help refill the board and the Mules that help refill the hand.

I mean, if controls manage to have all kinds of answers and/or we brick, it's just helpless for us, and it's totally okay cause that's how the matchup is supposed to work. BUT Aggro Taunt Druid doesn't come with 0 chances of getting through those matches. It actually has pretty good refill/comeback chances vs. control if compared with Shadow Priest or Face Hunter, which are way faster at eating HP but once they fall behind it's much harder for them to recover unless they have already dealt a significant amount of damage. Even if my stats aren't very significant (29 games are definitely not enough to fully evaluate the matchup trends), it's mildly shown that these matchups aren't this oppressive.

Also, if your pocket meta is crawling with controls, maybe there are much better decks to climb with than Aggro Taunt Druid. 

Glad to hear that! Wish you the best climb :) 

Hi HearthPillow, thank you for sharing your thoughts! 

Honestly I have never tried Blooms cause on paper they have just one pro that imho it's too mild to catch up with their two big cons. Yes, they can enable big tempo swings such as the one you mentioned, but at what cost?
- First of all, I believe that 2 Overload for a deck that just does one thing, namely developing board by playing cheap minions from hand, could be nothing less than crippling vs. control, since if what we have done with our Bloom gets contested, our next turn risks to be so crappy that it may cost us the whole game (control matchups are all about constant pressure, giving them just one turn of stabilization is hella dangerous).
- Also, based on my experience, this deck dramatically excels at winning the board in board-focused matchups (I think it would only lose to Rush Warrior if it was a common deck), so I don't think that +2 mana for a swing turn might be that helpful in these games and, combined with Overload and the fact that after turn 5 Blooms are a dead draw, I wouldn't run them. However, having never actually tried them out, these are just theoretic thoughts so I may be wrong, but there aren't definitely good premises.

Regarding Brawler, I think it's the most powerful 2-mana taunt we have since it can spiral so bad for the opponent, be it through value trades, Augmerchant or Kodo. 

Sorry for not inserting correctly the link/images of the proofs. Here's the imgur: https://imgur.com/gallery/8fQkUNj