Empty Hand of the Gods
This list is a first draft that no doubt needs tuning, but test draws indicate that it is quite powerful. The central concept is the revival of the classic madness engine, with Honored Hydra doing an impression of Roar of the Wurm, Noose Constrictor representing Wild Mongrel, and so on. By itself, this is pretty-good-but-not-good-enough, since your creatures are only a little better than they used to be, and everyone else’s creatures are much better than they used to be.
The key to making it work is that we also get to play the empty-handed strategy with Hazoret the Fervent and Lupine Prototype, and that in turn enables Rhonas the Indominable, which also gets help from Bloodfury Militant, Honored Hydra, and in a pinch Noose Constrictor. The deck has 14 creatures with a default 4 power that are not Rhonas the Indominable. When it needs to, it can also pump Noose Constrictor. Rhonas the Indominable gives you a mana sink with an empty hand that gives your other creatures trample, and will usually get to attack on turn 4 if the opponent does not use removal to stop you. Later in the game, you will get the two-God punch of Rhonas the Indominable and Hazoret the Fervent, with Rhonas giving tramp to Hazoret, which gives you a strong late game against anyone who can’t kill indestructible creatures.
A lot of good things can happen to you when playing this deck. You can win games by playing powerful, cheap creatures quickly and attacking—frequently with Gods attacking right on schedule. You can win games by using 1-mana removal spells to clear a path for your creatures. You can win by playing an upper part of the curve that some opponents have no answers for or that is more powerful than they can handle. You have plenty of enablers, with 19 cards that serve as discard outlets. You only have 8 cards that themselves benefit from being discarded, but given that many of the discard outlets cost mana to use, I did not find that there were others worth using. Incorrigible Youths is not terrible in theory, but it is difficult to use well and would often make it hard to empty your hand efficiently. You are playing good Magic, and I would rather play more good cards and have solid mana than reach for something lousy.
I considered Kessig Prowler in order to empty your hand faster, but I discovered that it was better to use Oath of Nissa on turn 1 to find the right piece of the engine than to play a random additional creature, even if it did work well with Rhonas the Indominable and give you another way to put your cards on the table quickly. I found that missing land drops was often painful, so Oath of Nissa is also necessary to give you some control over that, and a fourth copy would be very reasonable. Heart of Kiran is tempting because you have a lot of creatures that can crew it, but I think I would rather have additional attackers than tie one up activating the Heart of Kiran. Finally, it felt weird not to play Lambholt Pacifist, given the deck has so many ways to allow it to attack, but in the end I didn’t see a 3/3 (or even a 4/4) as being all that impactful and it does not help with either side of the engine, and it only half enables Rhonas the Indominable (even if Rhonas the Indominable enables Lambholt Pacifist). But if Lambholt Pacifist ends up sneaking in there eventually, that wouldn’t surprise me.
For the sideboard, you need to handle three basic cases: Saheeli Rai, Mardu Vehicles, and a deck against which your removal is bad. You need the removal in the main because it is naturally good for you and it responds to Saheeli Rai, but if you meet a control deck it needs to go, there need to be 8 cards to bring in.
The classic responses to Saheeli Rai in these colors are Walking Ballista and Shock. I am not thrilled with Walking Ballista, but everyone seems to love the card, and getting your removal onto the table is key in case you want to empty our hand, so you have little choice. You can scale back your main engine somewhat to get the removal, and still have threats big enough to overpower the enemy and enough discard outlets. 2 Shock seems like the most you can benefit much from, given that you already have Lightning Axe and you often want to be empty handed.
Against Mardu Vehicles, Mangehorn seems like the natural choice. You can find it with Oath of Nissa, it lets you gain advantage, and your creatures should be good at answering Gideon, Ally of Zendikar, so you are putting your worry in the right place. If your removal is bad, then what you do next depends on whether Mangehorn has targets and if you can go after Drake Haven, which is why Heaven // Earth is exciting. If none of that is interesting, you’ll have one awkward card, but keeping 1 Fiery Temper seems unlikely to be too bad. You’ll be stuck using Walking Ballista against control, but that seems totally fine. A few 1-of, generally good cards round out your board and give you some flexibility.