V1.11 - The meta is way more aggressive than it was during initial testing. Ramp seems way more important so I added another [humble naturalist]], and they work better with moth since now you can trade off your mana creatures and charming princes to stall the game AND now you have more bodies to get pumped by the End-Raze Forerunners. Tested Elite Guardmage and it just never did enough to slow down opponents that are really aggressive, since it's statline just does almost nothing in 90% of the matchups I played. Added Kogla over [[dream trawler and it was a slam dunk in 80% of matchups, since so many games are decided by 1-2 enablers now (Priest of Forgotten Gods, lurrus of the dream den, Risen Reef, Luminous Broodmoth, etc.).

Also, fixed the manabase and went to 26 lands. Can't believe I didn't do that sooner lol

Also, updated the video to closer reflect the current list!

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V1.1 The vid no longer matches the decklist and will be updated shortly with the new list, but is still a very strong list =) Bo3 list may be coming soon if in high demand =)

Here's just my observations of the deck and reasons for the cards I have in it after testing thus far:

TL;DR - At least 12x 2-mana ramp spells seems infinitely important, companion versions are clearly superior IMO, and Flex slots seem to be Dream Trawler, the 2nd End-Raze Forerunners, Migration Path and Luminous Broodmoth. Possible alternatives are listed below. Black seems not worth the drop in consistency of the manabase, and white has better cards so sultai seems worse. Possible alternatives are listed below.

----------------Ramp------------------------------------

First of all, ramp is super important to have at least 12x of since the effect of having a companion mitigates the inherant risk of running too many ramp creatures. We always have our payoff, and casting it turn 4 consistently is super important and leads to so many free wins.

Growth Spiral - obvious 4x in every ramp deck

Paradise Druid - Creature that can be grabbed by Gyruda in worst-case scenarios and can't be interacted with before you untap barring something like Angrath's Rampage. Also allows you to use things you can grab from opponent's decks like attack triggers from if you steal a Polukranos, Unchained or something from an opponent's deck

Wolfwillow Haven - this is considered a flex slot I suppose. I like haven because it's a 3rd ramp spell that's extremely unlikely for your opponent to interact with. Otherwise you may consider cards like Incubation Druid since you can get them from gyruda triggers, which are extra valuable when you also run Luminous Broodmoth which can give it more resilience.

Migration Path - Currenly running a 1x in my flex slot, but I've seen people running up to 3x. Seems important if people find more ways to interact with your early ramp spells, but will probably will replace this with a creature if the meta has less interaction.

----------------Other Creatures  (the obvious staples) ------------------

Gyruda, Doom of Depths - namesake of the deck and absolute powehouse. Can add like 30 power to the board on turn 4. Degenerate card that we get to cast every game. I've seen some people not running it as a companion and I think that's a HORRENDOUS mistake. It solves the ramp problem and we still have plenty of super powerful cards to grab. Plus, you can add odd CMC cards from the sideboard! Also it can't grab odd cmc creatures from its ability, so just doesn't seem worth.

Thassa, Deep-Dwelling - obvious staple as an indestructible blocker, surprisingly useful to tap down opposing creatures, and blinks Gyruda

Spark Double - Biggest enabler of the deck, letting you get extra gyruda triggers and add power to the board while doing so

Charming Prince - If you're bant, this is an obvious pick to help get extra triggers, and a reason to go bant or 4c over sultai

--------------------------------Contested Creature slots/flex slots------------------------------

End-Raze Forerunners - Important way to end the game quickly during a board stall, or end it early with a turn 4 gyruda, allowing you to attack for +9 damage or lethal on any following turn! The deck can get milled before pushing lethal if you don't have something like this to push through board stalls or after whiffing too many gyruda triggers. I think you need it, just debatable if you want 1-2. Also, you hard-cast it way more than you expect. Even works well with all your mana creatures and charming princes!

Dream Trawler - A good way to give your deck some presence in the air and longetvity after your opponent stabalizes. Good lifegain after stabalizing vs mono red and draws you into more powerful effects vs a highly interactive deck, while being able to protect itself from that interaction. Feels good but can depend on the meta if you want it over some of the other more interactive flex creatures

Fblthp, the Lost - Could be used to lower the curve and help you hit your land drops. It does not draw 2 cards from Gyruda since it is put into the graveyard before entering the battlefield. I think the ramp is more important and if we're not hitting land drops we can just up our land count. We need to hit gyruda as quickly as possible, and Fblthp doesn't help with that. Companion gives us consistency, so we need ramp, not extra consistency. Is a good thassa/charming prince target though, which the deck doesn't have a ton of though, so might make it into the deck once the meta adapts and we need more avenues to accue value

Kogla, the Titan Ape - can fit in the slots over Dream Trawler or End-Raze Forerunners if you need to be more interactive. Also can protect itself from a sweeper by bouncing a Charming Prince or something. rare, but it comes up lol. But a creature you can fetch that affects the board in terms of fighting creatures and with a built-in naturalize effect is nothing to scoff at. Definintely something to consider depending on the meta, and with more Lurrus of the Dream Den oven decks coming up, it can be on the upswing

Luminous Broodmoth - EDIT: more underwhelming after more testing. The meta shifted to more aggressive matchups rather than more grindy matchups, and it doesn't affect the board enough. Could be better in a more creature-heavy build. I'm now trying 14 ramp spells and flirting with 10 of them being creatures so curving intot the moth is better and allows you to chump block. Not sure if it's worth it though. This deck has so many slots that then inform other deck slots, so the versions with moth should look very different in my opinion. But now I consider it just a 2-of at most probably. My biggest regret for not testing during the streamer event. Seems like a slam dunk by turning your legend-rule-deaths for Gyruda into more triggers! also gives them flying to mitigate the board-stall problems the deck can have, AND insulates you against sweepers! My only concern was adding a double White mana cost to a splash color, but with paradise duids and all our dual-lands it should work. You can even run incubation druids if you're concerned about the mana. Seems like a slam dunk for the time being, until people start running maindeck Extinction Events XD

Dream Eater - Thought this was pretty good and possibly a good slot until I saw Kogla. Kogla hits creatures and can kill artifacts and enchantments. So the only thing it can hit that kogla can't is planeswalkers, or creatures bigger than 7/7. Surveil 3 can set up Gyruda triggers, but Kogla's impact is usually enough that you don't need another trigger. It has its place sometimes though, definintely keep it in mind.

Elite Guardmage -EDIT: Guardmage seems like a fine placeholder, just don't think it's an automatic 4-of, but I do recognize the lower floor on broodmoth is a legitimate concern.  I see so many people run this card and I'm not sure it's good enough to warrant it. Moth does SOOO much more to keep your deck resilient than drawing a random card, but it certainly has a lower floor than guardmage, so this acts as the safer option i suppose. Dream trawler is lifegain/card advantage, and if you reeeeaally need lifegain that badly there's better options. The deck would rather play cards that ramp them to 6 mana on turn 4 (can change in Bo3, where this could be a good sideboard card against more interaction), and there's way better gyruda targets. Definitely can have a place in the deck, just seems like a meta call to me if you want the deck to be more midrange-y vs combo-y.

Dungeon Geists - Another cheap interactive card you can hit off of Gyruda, also has evasion. Seems like a decent interactive spell that's easier to hard-cast than things like Kogla.

Umori, the Collector - Can't be your companion since you already have one and play noncreature spells, and this deck is more of a "tap out to play 1 big creature" type deck rather than a "draw multiple cards while deploying cheap threats." IDK, seems kinda meh vs the other amazing plays we have. I mean there's no way this is better than broodmoth, right? Maybe in sultai versions... maybe... XD

Sphinx of Foresight - Could be a decent pick for the version of the deck that's ALL IN on the combo and doesn't care about resiliency. Combo gives you perfect percentage of draws with a payoff, and the scry 3 can help make sure you get 2x 2 mana ramps spells for a turn 4 Gyruda. Maybe if the meta gets so degenerate that interaction and resiliency aren't as valuable (which is very possible in current standard, mind you) then this could be considered for the deck

Loxodon Lifechanter - Bet most of you forgot this card existed, as did I. But with how many days I vs mono red like 3-6 times in a row, I thoght it'd be valuable to just have it here as an option. Hitting it off a gyruda would allow you to get your life to a mininum of 12, and max of like +30, so could replace some forerunners or something if all you're facing is mono red. Part of me just wants obscure cards to see more play, as jank is my calling in life XD

Questing Beast - Seems good in a deck full of 12x 2-mana ramp spells, and a decent hit off of Gyruda in matchups where you need to be the aggressor and your opponent is using planeswalkers or chumping creatures to stave you off. Maybe better for sideboard.

Gargos, Vicious Watcher - maybe some case could happen where he's better than kogla? Dunno, just thought I'd do the thinking for you in finding alternatives, but seems less versatile and impactful on the face of it.

------------------------Why Bant instead of 4c or Sultai? AKA Black flex slots-------------------

Polukranos, Unchained - Seems great for more interaction and can come back on its own. Works whether milled or drawn: Definintely a big reason to go black

izoni Thousand-eyed - If you go sultai it could replace dream trawler for card advantage and works better with end-raze forerunners. Also, blinking it with thassa is hilarious

Blood for Bones - Great way to get extra gyruda triggers and rebuild after a sweeper or something after leaving an extra mana creature in hand or something. seems better in 4c to me since returning Gyruda to Battlefield and then getting a charming prince into hand seems nuts, but if you have +8 mana you can just hit gyruda and play a spark double or something too. Seems too cute but could be good.

Atris, Oracle of Half-Truths - Seems cool in the blood for bones verison of the deck or something, where you can get back the cards from the yard. Also helps fuel polukranosl. Seems cool in a slower meta as a grindier card.

Yarok, the Desecrated -saw people saying he's good here. I love him more than anything, but even I can see that's not the best. has to be sideboarded or in a non-companion deck. Not worth losing companion and can't get hit by Gyruda's trigger either.

All in all, white just has way too good of cards in things like broodmoth, charming prince, and dream trawler to remove white IMO, but there could be arguments to 4c. I think the strength of the deck is in its consistency and ability to take advantage of the companion mechanic, so adding a 4th color and reducing consistency seems unintuitive to me. It certainly can be done, just not sure it's worth the cost.

Hope at least some of this was valuable lol.