With everyone playing questlines (mostly Mages and Warlocks) I thought really hard how to counter their decks since they promote such an uninteractive matches. I tried going hard control with Priest and Warrior with as many anti spell minions like Ogremancer and Cheesemonger with no luck. Mages and Warlocks can always clear the board and outlast me. I thought I could eat away their quest reward with Mutanus the Devourer but a good opponent will always clear the quest the same time he can play his minion reward to avoid such situations.
So how can you delay your opponent from finishing their questline and prevent them from playing their quest reward? Enter Celestial C'Thun Druid.
Celestial Alignment one of the key elements in the deck. Playing this before your opponent finishes their last quest will set them back to 1 mana leaving them unable to play their reward as it will cost 5 mana by the time they finish it. Lady Anacondra and Gadgetzan Auctioneer combo are your main win condition in assembling and playing C'Thun, the Shattered in one turn by cycling all the nature spells with Innervate and Lightning Bloom reverting to costing 0 mana post Alignment. Once you cast all parts of C'Thun, the Shattered you should play the other Celestial Alignment and set everything back to 1 again.
You want to keep a large hand most of the time. If you are low on cards then can use one of the Nourish or Gadgetzan Auctioneer with cheap spells to cycle through your cards. Malygos the Spellweaver is an excellent refuel card. If you have Goldshire Gnoll in hand then you can play it for 1 mana to avoid card burn after playing Malygos to fill your hand.
For defensive options that will help you past 7 mana you have Cenarion Ward. When combined with Solar Eclipse you get 16 armor and double the chance of getting one of two best defensive random 8 drops Mo'arg Forgefiend and Taintheart Tormenter. It is important to note that both Cenarion Ward and Solar Eclipse are Nature spells so if you have Lady Anacondra and Gadgetzan Auctioneer combo, chances you can steal away the win right there.
I included 2xGoldshire Gnoll in this deck because if you have just one other card in your hand, you can play them along with Celestial Alignment as they will cost 0 mana. Flightmaster Dungar and Best in Shell are good defensive tools that can fend off aggro decks until you can plan a comeback. Delaying Flightmaster depends on how fast your opponent is dishing aggro, if your opponent is too aggressive then I would recommend prioritizing playing him as soon as possible. Best in Shell although not a Nature spell, the fact that it has Tradable make it valuable for recycling. It also can be combined with Solar Eclipse to create a heavy board in a pinch.
Lastly Shadow Hunter Vol'jin and Mutanus the Devourer are included to further mess with your opponent if somehow Questline decks are close in reaching 5 mana to play their minion reward post Alignment. These can be easily swapped for more defensive options if the meta gets more aggressive. 2xSpice Bread Baker or 2xArmor Vendor are both good. Although I didn't test it out myself but 2xMailbox Dancer could be worth considering as you might have more use out of the coins for ramp and cycling with Gadgetzan Auctioneer than your opponent.
You need to mulligan for your ramp up cards Wild Growth and Overgrowth as the majority of your deck depends on the late game. In some cases like when facing Questline Mage and Warlocks, you'd want to keep Celestial Alignment in your opening hand to ensure that you have a chance to cast it before they finish their last quest.
Celestial Alignment vs Questlines
Questline Mage: Generally it is safe to play Celestial Alignment especially after they used up their Incanter's Flow because it sets all cards back to 1. Remember that they can only play 1, 2, 3, ... and so on cards each turn from that point. Playing Celestial Alignment is top priority to prevent them from reaching the last reward as they are most dangerous post it.
Questline Warlock: Same as Mages but I recommend playing Celestial Alignment as soon as possible. The issue with Warlocks is that they can use health instead of mana with Stealer of Souls to bypass Celestial Alignment effect. Interesting to note that since all their cards cost 1 mana then they will inflict only 1 damage to the Warlock. This delays them incredibly so but be careful as they can still win by fatiguing themselves.
Questline Hunter: Same as Mages but less dangerous if you didn't manage to play Celestial Alignment before they complete their last quest.
Questline Priest: Funny enough, it is almost impossible for them to complete the quest post Celestial Alignment as everything is set to 1 mana (There is currently a bug where their questline still counts the original cost of cards rather than the 1 mana set by Celestial Alignment). Even if they manage to complete the quest, remember they can't play their reward in the same turn. If you set their reward minion to 1, the Purified Shard cost 10 mana.
Other Questlines are generally not affected by Celestial Alignment and they aren't a priority to delay for your opponent.