Things to remember:

Starting hand must ALWAYS have an elf, and 2 green mana sources (don't count Nykthos as a land). Otherwise you may be stopped at turn 2 with no card to play (given that elf can be Fatal Pushed)

Depending on a Match-Up, you usually want to place Tribute to the World Tree first, then any other creature. Tribute is way harder to remove than creatures and it still drives your Nykthos into a ramping mode. Obviously you put creature first when you are against mono red or other quicker aggro. 

Now about the cards:

MAINBOARD:

1 drops:

Elvish Mystic + Llanowar Elves = obvious pick for starting hand, having 1-2 of them is a sign of a great start and a signal to your opponent that his counters/removals won't stay in his hand for long.

2 drops:

Werewolf Pack Leader great follow-up for that Fatal Pushed elf from turn 1. Gives 2 devotion, a great body to attack/block. It's quite mediocre against mono Green Devotoin (the deck we all know) which puts Old-Growth Troll at turn 2. Still, you need bodies and devotion. Period.

Voracious Hydra mostly used as a 4+ drop, but there are scenarios where you can put in in play on turn 4+ for just 2 mana nad have so much value that your opponent will consider conceding.

Invasion of Ikoria // Zilortha, Apex of Ikoria as previous card, it will be played in later turns due to X being mostly 3-6. Purpose of this card is to tutor creature you need the most = especially after sideboard (you can consider creatures that are artifact/enchant hate, fliers hate etc.) If you manage to flip this, opponent will most likely to just count your creature power against his leftover HP.

3 drops:

Old-Growth Troll Dragged here from mono G Devotion deck, he's doing so many things, that he cannot be replaced. He ramps oyu on death by sticking to Forest. He has Trample. Is a 4/4 for 3 mana. He's very close to be called a Green Staple.

Polukranos Reborn // Polukranos, Engine of Ruin POWERHOUSE-HYDRA. He is to be flipped as quickly as possible, BUT you must remember that flipped Polukranos gives no devotion (yet it's mana value remains 3). Polukranos is a backbone of this deck, giving you devotion on front side, a reliable blocker against most aggro decks and option, to create a setup, where opponent thinks only of removing him.

Flipped Polukranos have a godlike synergy with few cards in deck. 

With Voracious Hydra you can fight creatures and end up with getting 2 3/3 tokens thanks to Polukranoses static ability. It additionaly goes great with Tribute to the World Tree but I want to talk about it later.

With Lair of the Hydra you can have a blocker/finisher, which can also crack into 2x 3/3 tokens (Lair is usually Fatal pushed after becoming a creature - and I know, that Polukranos can be pushed also, but it needs a 'revolt' active).

With Mistcutter Hydra a sideboard position I will definetely have a 4of; This hydra is a very flexible option. It can be a full mana finisher, or 1 mana 0/0 which cannot be countered and instantly becomes 2x 3/3 Tokens with Polukranoses static ability.

Tribute to the World Tree not gonna lie - when I first saw that card (and Polukranos) I was already thinking of "all-creature" deck.

I started by creating a RG aggro deck which used creatures to find lands, and big stuff like Dragonlord Atarka or Ruric Thar, the Unbowed but I ended up with so weak score, that I scrapped that Idea just dayu after.

With this deck, Tribute can land as quick as turn 2 on board. It makes your 2+ Creatures draw a card each time they enter the battlefield, and you want that! Oh those draws! Important thing to remember is that when you have TWO Tributes, they work separetely. When you play an elf with two Tributes in play, you first put 2x+1/+1 counters, which makes Elf a 3/3 and then you draw a card, from second instance of another Tribute.

The same goes for Voracious Hydra - but you can have more options. Let's say you have 2x Tribute to the World Tree in play:

• playing Voracious Hydra with X=0; gives you a Hydra 4/4 which can fight or double its counters
• playing Voracious Hydra with X=1 or 2; gives you a hydra 3/3 or 4/4 which can fight/double its counters and additionally it will draw a card
• playing Voracious Hydra with X=3+; so it will enter as a 3/3 which can fight/double it counters and draw 2 cards

Very flexible, don't you think? Especially when Polukranos Reborn // Polukranos, Engine of Ruin is in play flipped, than you can also try to work around fight part where Voracious Hydra will die and trigger 2 tokens which will draw more cards. So many draws!

Augur of Autumns - Firstly, in my deck there was a Courser of Kruphix which allowed me to play lands from library and gain some life. His issue was that he revealed top of my deck, and my opponent would play around my draws. Augur skips that, you are the only one who konws what comes from top at any time but with a downside that it won't give you life from played lands. Another downside of Augur is that his toughness is 1 less than Coursers. Significant for aggro match-ups... BUT! There is also an upside. A very imporntant one that I was totally unaware of - when having on board 3 creatures with different powers (which isn't really a hard condition to provide) you can also play CREATURES FROM TOP OF YOUR LIBRARY - and this is where Augur Shines like a gold. With Tributes in play, Nykthos which probably gives you already 9+ mana, you will notice that you're able to cast creature after creature from top of your library and draw significant amount of card thanks to the Tribure. In few cases it felt like some kind of infinite combo. Very good card Which I'd like to have more in main deck.

4 drops

Vivien, Arkbow Ranger - taken from a stompy version of mono G devotion Deck, Vivien provides 3 devotion, removal, and can pump up creatures which can defend her (this is usually the way I am + her). After one or few turns with her on board you most likely have a nykthos in play with so much devotion that you can activate Nykthos, -5 Vivi and look into your sideboard for game-ending option to cast. There are osme match-ups where +ing her is enough to take over the game.

5 drops:

Silverback Elder - as much as I'd love to have more of him, I'll probably cut him to just 1-of in deck. He single-handedly transforms your creatures into Ramp/Disenchant/Lifegain spells. If you played long enough to have also Tributes/Augur in play - game becomes ridiculous concert of spell casting with triggers.

6 drops:

Vorinclex, Monstrous Rider - 1of, but mostly a 2-of in stompy version of old monoG Devo deck. I've struggled and decided to have 1 Vorinclex and 2 Monkeys, but after last tournament I'll most likely take a step back and put 2 Monstrous Riders in main deck. What he does with Tributes, is a joke. Even a single 1drop elf, can become a 5/5 beast which can beat-up quite fast. I won't even type what it does with Voracious Hydra or Vivien, Arkbow Ranger - that is something you just need to see or play yourself ;)

10 drop:

Ulamog, the Ceaseless Hunger There is no Szmaglord's Deck without Ulamog. Force to be reckoned with, Ulamog just waits for that tenth mana available to end your opponent dreams. By the time you're ready to play him, your opponent probably already struggled with all previously mentioned cards. Seeing this Eldrazi Titan (and it is the smallest of three!) will most likely make your opponent extend their arm and say 'Ok GG'. It fells so Timmy, it feels so goddamn good ;) Also there is another one in Sideboard to search with Vivien when you happen to have like 10+ mana from Nykthos on turn 4 (it is doable, trust me).

LANDS:

What - you think this is an obvious part? Sure, 10 basics are not something that I can talk much about, same goes for Nykthos - we all already know what it does. 

We can even say that Lair of the Hydra is quite obvious - it combo'es with flipped Polukranos Reborn // Polukranos, Engine of Ruin.

Boseiju - sure, we can think of many targets for it, play one, keep the other for Channeling.

buuuut...

Castle Garenbrig is a pretty neat card. "I don't know, it just adds one additional mana and let's you cast only creatures". Yes and No, there is a bit more to that. When you have Nykthos with, lets say 8 devotion, 2 castles and two Forests, you can activate Nykthos for 8 Green, and use it to activate both castles, giving you 12 mana for creatures from just 5 lands. And this happens quite often, trust me. Having mana "ONLY" for creatures may look like a downside at first, but after realizing that deck contains 29 of them, and you have AT LEAST one Tribute to the World Tree in play, it becomes a one big grind. Not to mention the ridicule when Augur is present on board...

Sideboard:

Is still a work in progress.

For now I've chosen:

Scavenging Ooze as a graveyard hate.

Mistcutter Hydra as a control/spirits/blue decks hate

Arasta of the Endless Web as a combo/control/fliers hate

Barrier Breach cause sometimes Enigmatic Incarnation and it's leylines is a nuisance

Obstinate Baloth cause discard can happen  (especially against any black deck)

and then there is a Vivien-board, utility high-end creatures, where you just grab one when needed, with one case of creature that I put in Main at game 2/3 against control decks, and this card is

Tyrranax Rex - which is great, due to his Ward 4, what makes him mostly out of reach against Wandering Emperor

rest of the best:

Ulamog, the Ceaseless Hunger, The Tarrasque, Titan of Industry, World Breaker

Changes are to be applied soon, as I want to try this deck at least few more times at my LGS, and I'll definietely use it to grind Arena's Explorer.

----

 Score to date:

24.04.2023: 4-0-1 (split)

Round1: vs neoform Atraxa, G1 I've manages to survive untill his deck runs out of cards, G2 - we both mulled to 5, but his hand was slow, and mine was just creature after creature and I've managed to stomp him

Round2: vs UW Control, G1 I've stomped quite hard, was quite lucky in my opinion. G2 - I went all in putting down 2 elves and Wolf, and then Nykthos Into Tyrranax, which came after sideboarding. I was expecting Supreme Verdict on opp's turn 4, but he didn't have it - he was waiting with emperor, and thanks to Tyranaxxes ward I've managed to win this.

Round3: vs Mono G Devotion, another unfavourable match up in my opinion, I've managed to grind him out on G1, lost to Kiora/karn combo in G3, and do it again (grind him out) on G3. My opponent just missed good-drops with his Festival. I had Augur, Tributes and monkey - and so much has happened that I just couldn't lost it.

Round4: vs Mono G Stomp, basically a mirror match - we had a difference of 6-10 cards? He used Oath of Nissa and I've used Tribute to the World Tree. No to drag or brag to much - I've just been more lucky, drew more cards. There was a pretty neat play from my opp where he had 1 land for 3 turns, and he managed to play 3 elves, 3 Burning-Tree Emissary and Vivien - and then on turn 4 or 5 he just TOPPED Nykthos... He was at 13 devotion, and he could win that, but he didn't have an Ulamog in his SB. It was scary.

Round4: vs Imperiosaurus Combo. We've played for fun, we took split. After getting bonkers with my green broccoli stuff, opponent showed me a true power of imperiosaurus casting him in turn 4 as a 18/18 and attacked me on turn 5 for lethal. And he did almost the same G3, when he played one after another, and gave him haste. This deck is BONKERS. I'm not sure if I would play it in paper but I will try it out in Arena most definetely :)

What do you think? Do you see a way to upgrade or change something in the deck, have you played it yet?

I'll probably will try it out live, or do something fun somefar soon on my twitch channel: https://www.twitch.tv/Szmaglord

Thank you for attention :D