Disclaimer: This guide will be updated when the new expansion launches. Different matchups and card replacements will be included once the expansion is released depending on the changes to the meta.
The main idea is to use the synergy between your elementals for board control. And later on winning the game with Hagatha the Witch and strong elemental minions. Additionally Shudderwock is a nice late game win condition which makes the deck even more fun!
Hagatha the Witch combos nicely with Bogshaper as it allows you to get more card draw (which prior to the Witchwood was one of shamans weaknesses). For every minion you play you get a free shaman spell and for every shaman spell you cast you draw another minion from your deck. Unstable Evolution is also very strong with Bogshaper since you draw a minion for every time you use Unstable Evolution. You will want to use Unstable Evolution on a minion with suboptimal stats due to its battlecry (e.g. Stone Sentinel).
Shudderwock works nicely with all the battlecries which you get due to your elementals. Of course this is no OTK deck and Shudderwock isn't always going to work in your favor but I still believe it is a good card to have in your deck since it will make your games much more fun and is more likely to help you out since you don't only have 'Deal x damage' battlecries but also summons and heals. Another upside of this deck over an OTK Shudderwock deck is that you dont rely on drawing your combo pieces as heavily.
Grumble, Worldshaker is used for getting the battlecries of your minions on board another time and also refreshing their health for little mana. Additionally a 7/7 body is nice to have when your board is mostly empty. Additionally you will create a spell for every minion you play after reducing their cost to 1 mana when combined with Hagatha.
Kalimos, Primal Lord should be an obvious pick since he works really well in elemental decks. He pairs well with other elementals in the deck like Grumble, Worldshaker enabling you to choose from his battlecry twice and healing him back to full health.
Al'Akir the Windlord is optional, he can easily be replaced by other cheap elementals or even Ozruk with some minor changes to the deck if you don't own the card. It isnt an essential combo piece like Hagatha the Witch or Kalimos, Primal Lord but it is good at removing multiple weak minions or a low health high attack minion due to Divine Shield, getting in some face damage and protecting yourself with a Taunt + Divine Shield minion. It is just a minion which can serve multiple purposes and it being an elemental is the cherry on top of the cake.
Fire Plume Harbinger helps you get out more elementals. It is especially strong if you have many minions in your hand. This will happen if you combine Bogshaper with Unstable Evolution or after using Grumble, Worldshaker for free Battlecries and a health restoration for all your minions on board.
Lightning Storm, Hex and Volcano are there to reset the board in your favor without any setup in the earlier stages of the game. Running Hex twice should also be a good idea since it is a hard counter to the most prominent deck at the moment, control Warlock/Cubelock, which will probably be around for a bit longer. Using Hex on demons also denies the Bloodreaver Gul'dan battlecry since it only summons demons, which died this game and hexing a minion doesn't count towards that.
Murmuring Elemental is a key card in this deck since it allows you to trigger a Battlecry twice. Since the most expensive cards in this deck cost 8 mana and Murmuring Elemental is a cheap 2 mana minion you can combine it with every Battlecry card in this deck. Since there are so many Battlecry cards in this deck I will only cover the most important combos; If you combine Murmuring Elemental with...
- Fire Plume Harbinger all elementals in your hand cost 2 mana less. With a big hand you can cheat out many minions alot cheaper or just a big minion like Al'Akir the Windlord or Kalimos, Primal Lord earlier in the game.
- Stone Sentinel for a big Taunt wall.
- Hagatha the Witch for boardclear.
- Kalimos, Primal Lord for a double Elemental Invocation. This can range from 6 damage to all enemy minions which will clear almost the entire enemy side of the board in most cases to 12 damage to the enemy hero or even a 24 health heal to your own hero.
- damage battlecries for twice the damage (e.g. Blazecaller).
- Servant of Kalimos for two elementals instead of one.