I made this deck because I was sick and tired of the amount of Shamans I encountered on ladder. I took the standard Highlander Hunter package and removed some of the lower winrate cards for some more tempo and draw.

Cards I removed from the 'standard' list:
- Ursatron
- Ragnaros the Firelord
- Sandbinder
- Shimmerfly

Ursatron and Sandbinder are draw, but I have always prefered the draw engine that Cult Master delivers. With Snake Trap, Unleash the Hounds and Swarm of Locusts in the deck, it's quite easy to draw 4+ cards in a turn. Plus, my version of the deck is to always have either board control or board clears. That means you often start with minions in play and thus potential Cult Master draw.

Ragnaros is simply not a great card in this meta. You often face very wide boards of small minions, where paying 8 mana to kill a 1/1 simply isn't going to win you any games. Similarly, this deck doesn't need Thaurissan or Sylvanas as they are low tempo value cards. This deck needs Tempo, Tempo and more Tempo.
So, I replaced Rag with Swarm of Locusts as that often clears Shaman boards and can combine very nicely with Timber Wolf, Animal Companion (Leokk) and even Zephrys the Great. More than once I was even able to play Swarm of Locusts on 6 and follow that up with a turn 7 Zephrys into Bloodlust lethal.

Finally Shimmerfly I just replaced with Hungry Crab. Since I mainly face Shamans and all Shamans run murlocs, this comes in handy quite often. However, you can easily choose to keep Shimmerfly over Hungry Crab. Another option is to play Scavenging Hyena in this slot, as that could also snowball quite quickly.

I feel my changes have made the, already quite good matchup, against Shaman even better. I've won about 70-80% of matches against Shaman decks.

Mulligan Guide:
You always keep high-Tempo early plays, like [Hearthstone Card (Secret Keeper) Not Found], Springpaw, Desert Spear and even Subject 9. Rat Trap and Snake Trap are also solid keeps, as it can take a few turns for them to trigger, giving you time to get value out of Sunreaver Spy, Masked Contender and Hyena Alpha.

Versus Shaman: I like to keep Snipe to kill their EVIL Totem, Hungry Crab, Animal Companion, Unleash the Hounds and Houndmaster. Basically anything to get on the board quickly and stay there.

Versus Paladin: as this is a very difficult matchup in most cases, I try to overwhelm the opponent as quickly as possible. Keeps here are Rat/Snake Trap, Hyena Alpha, Zephrys and even Dinotamer Brann.

Versus other decks: it depends a little on what you see on ladder, but I often go for maximum Tempo. Mage doesn't get good clears until turn 6; Warrior is a joke, as are non-Zoo Warlock and Rogue decks. Quest Druid is about 50/50 and comes down to pressuring them in making sub-optimal plays. If you can't win by turn 7 or 8, you won't win at all (unless you can do turn 9 Call of the Wild into turn 10 Zul'jin).

Apart from Paladin, the only truly difficult matchup is Resurrect Priest. If they can establish board, you're not going to get through. Wait with Zephrys for a turn to push lethal, or silence the entire board. I once one by keeping a Convincing Infiltrator alive on the board for 3 turns, just to steal it with Zephrys into Cabal Shadow Priest.

In the end this deck walks the fine balance between trading for Board Control and pushing face damage for lethal. Play it a lot and you'll get better at it quicker than you think.