This one is a work-in-progress. Seriously, CRAFT AT YOUR OWN RISK! There are some niche cards in this deck.
UPDATE - 6/21/20 Below
The true goal is to make a deck that is decent using Jungle Giants. There are so many options here imo. I'm trying a beast synergy deck. Marsh Hydra seems to fit well because it gives you value and it is a big minion with Rush. Oondasta is pretty good in the deck as well. He has Rush and he can pull a beast from your hand. The main issue with this deck is obviously aggro, so getting Rush minions on the board can really help.
Most decks can handle one big minion per turn, especially in the mid-late game. What wins games is the swing-turn....when you can put two or more big minions on the board at once. But don't over-commit! Often two or three are enough to cause issues. It depends on your opponent. Plus. you can usually reload next turn. Creating multiple "small" swing turns is usually better than one big one. Although, there are prob exceptions here. Ways to pull out extra big minions is what makes Strength in Numbers, Giant Anaconda, and Oondasta all good imo.
Charged Devilsaurs are nice because they can get "cheated" out many different ways, not triggering it's battlecry which allows you to go face. Strength in Numbers, Giant Anaconda, and Oondasta can all do this, if you're lucky.
I hope this explains the deck a little and why I chose certain cards. I may provide more card explanations later. I don't have a detailed mulligan guide yet. You can try to mulligan Jungle Giants against aggro, and that may be correct. Obviously you are looking for Oaken Summons in any matchup. Remember you have no 6-drop minions, but you do have plenty of 7-drops. So you can often play a 7-drop on turn 6 or sooner if you have Jade Blossom, Biology Project, or the Coin.
Good Luck Everyone!
UPDATE - 5/29/20
UPDATE - 5/30/20
I've played a few similar decks, and I'm trying to make this a little better. I don't think the Elder Longnecks are necessary for the quest. The Giant Anacondas feel great! Love that deathrattle. Menagerie Wardens just seem to fit this style. I know the deck should have a few 5-6 drops. Playing this on turn 6 feels alright even if you don't have a beast on the board. (It's not ideal obviously, but you have another one.) With so many beasts in the deck, there's almost always a target for this in the mid-late game. FYI - You can play it on Winged Guardian. And you should be able to play it on Charged Devilsaur and go face. There are a lot of cool interactions in this deck.
Usually I try to use Branching Paths for card draw after you complete the quest. Sometimes you have to use it early just to draw cards or armor up. Occasionally, if you have a board remember you can use it to give +1 attack to all your minions. You can also play it after you play a 0-drop rush minion for extra attack if needed.
Two Strength in Numbers felt like too much at times. That second one can get stuck in your hand or at the bottom of your deck. I'd rather have a Ferocious Howl or something I can play early. This deck just doesn't have room for dead cards imo. But I love the card, and I may try two again later. It felt like the best card to drop for now.
Ferocious Howl feels good. Not sure about Biology Project and Jade Blossom yet. At times this deck feels great, and at others....not so much. I'm working on a dragon version too. Maybe this has too much beast synergy?....I'm not convinced yet. More testing.....Good luck and let me know if you have any ideas.
UPDATE - 6/21/20
Ok...this deck hasn't been performing well for me. So I made a ton of changes and took the deck in a slightly different direction....trying to make the deck a little better. I may reverse a few of these changes, but I think most of them are good. Basically, I removed some of the beast synergy. I'll explain a little here:
I took out ramp for other early anti-aggro tools. I thought that Archmage Vargoth, Menagerie Warden, and the Charged Devilsaurs were too greedy. The Marsh Hydras feel bad unless you need late value. Oondasta only works with beasts, and I removed a few so that him worse. I hated removing a Giant Anaconda....he may come back. I also removed one Ferocious Howl to make some room. I still like two, but honestly I'm not sure even one belongs in here. Trying one out for now.
I added Lesser Jasper Spellstones, Wraths, and Starfall to help against aggro. I put in Stampeding Roar for something to play on turn 6. It works pretty well, but one is plenty. I also put in two Evil Hecklers to help with the quest -- not sure if both are needed though.
Zilliax is still good I think, so I thought it would help. I added the Evasive Drakonids and one Scrapyard Colossus to replace other big minions. They're both big taunts that can be tough to deal with.
I'm not sure all these changes are necessary, but I think the deck feels much better now. I still think this deck needs some help....I'll update if I get any more ideas. Thanks for checking!