Hello guys, thanks for helping this deck get to the front page! That's incredible. I have added a Mulligan section to this page to be a more complete guide as a thank you.
This deck is a Tempo Beast/Ramp/(Combo?) Druid, and I think it will be really fun to play and could potentially be a good deck as well!
With new cards like Oondasta and Stampeding Roar which can cheat out big beasts, and lots of ramp to use them quickly, this deck can make a lot of tempo plays and get a lot of value at 6+ mana, which Druid can almost always achieve by turn 4 or 5 to make it a viable archetype.
Predatory Instincts seems like an odd pick over other draw options that Druid has, and it isn't really a good card if it is only being used to tutor Hadronox. However, when doubling the health of ANY of the beasts in this deck, it becomes really powerful. Huge taunts or rush minions with high attack and high health are very strong, and your minions will be very hard to trade into and will need hard removal or silence to deal with.
Ironhide Direhorn originally seemed like a mediocre card, but if you can Stampeding Roar into a Direhorn with Rush, kill something, and summon a 5/5, that is a huge tempo swing and can win you the game against other tempo decks.
Charged Devilsaur is the best card to cheat out if you are looking to do face damage. It can immediately attack for 7 to face when cheated out, and if it was buffed with Predatory Instincts, it can do 14 damage because of being able to flip the stats with Crazed Alchemist.
One of the funniest combos you can pull off with this deck explains the reference "Ultra Instinct". If you buff Ultrasaur with Predatory Instincts, you get a 7/28 minion. You can cheat it out before 10 mana, and the opponent will most likely ignore a 7/28 with no taunt. The next turn you flip it with Alchemist and it is 28 face damage. This isn't usually going to win the game for you, but the possibility is too fun to resist, and cheating out a 7/14 really isn't bad either. You can also flip Ultrasaur for an easy 15 or 29 armor with Earthen Scales if you are just trying to stay alive.
Witchwood Grizzly is another good card to cheat out because you get rid of the Battlecry drawback. Resurrecting it with Witching Hour will also make it start with 12 health. If you use Instincts and get this card, it is basically auto-win against aggro if they don't have silence.
Juicy Psychmelon is a natural fit for this deck as you will draw 3-4 consistently.
Witching Hour is extremely powerful no matter what target you hit. At the absolute minimum, you summon a Ironhide Runt and only save ~1 mana, but 95% of the time, the beast will be worth at least 7 mana and save you 4-7 mana for an extreme tempo play. The only downside is that it is a dead card for the first several turns.
Spellbreaker is likely going to be a very important card in the upcoming meta as there will be several deathrattle based decks and it can also allow you to push through a taunt to finish the game.
The other card picks just synergize really well for a Druid deck that wants to ramp quickly and stay alive long enough to get some really strong minions on the board
Cards to Consider:
This deck might be too greedy in a fast meta, but will be amazing in a average or slow meta where you can play all your threats as soon as possible. If the meta is fast, there are other options listed below, but a lot of these cards could slow you down and cause you to not get beasts on the board as quickly or consistently.
Another Spellbreaker, Gluttonous Ooze or Harrison Jones, Chief Inspector, Mossy Horror, Void Ripper or another Crazed Alchemist, Crystallizer (if you add another spellstone), Arcane Tyrant, Untamed Beastmaster, Amani War Bear, or Giant Mastodon. Which cards heavily depends on what cards are defining the meta.
If you cut Ultrasaur, Crazed Alchemist, or basically anything else, you are playing this archetype very differently. I'm not sure if it will be worth trying to make this deck work in a super fast meta anyway, so don't try too hard to make this good against aggro.
It is usually safest to mulligan like it is an aggro or midrange match-up, depending on how aggressive the class usually is. It is also useful to know exactly what cards each class has been most often playing in the early game and if your hand will be good enough to handle it.
This can be a lot to take in if you are a newer player, especially if you aren't sure how to play against certain meta decks. A good place to check is HSReplay, where you can see what decks are doing the best in the current meta and how you can counter them.
These cards shouldn't be kept unless you have at least 2 of the cards above.
Tertiary keeps (only applicable if going 2nd):
If the stars have aligned, you have the coin, a good curve, and all but one card in hand is listed above, then keep one of these cards:
Against Aggro: 2nd Swipe
I really think this will be a fun deck to play and is a lot more interactive to play with than other Druid archetypes in standard and I am looking forward to trying out this deck! I hope you like it too!