Hi, I'm Gami and this is my Pioneer Stompy list! If you're like me and enjoy undercosted big green creatures, you're in the right place!
This deck is built to maximise Collected Company and Aspect of Hydra to outsize and outvalue our opponents!

Deck Info:

Noteable Inclusions:

Glissa Sunslayer - Glissa is one of the most powerful three drops in the format. They may not have the biggest stats, but they will trade with any creature that happens to be bigger than the rest of our team. They also act as removal for enchantments and planeswalkers and they can even draw cards if none of these are relevant. They're the reason I'm splashing black rather than any other colour here.

Collected Company - If you're playing the best three drops in the format, getting two of them at instant speed is often enough to seal a game.

Aspect of Hydra - This is a card that will most often win the game if the creature connects. It will usually be +7/+7 or more, making a previously unassuming attack into lethal. It's even more potent when we're only running 7 permanents that aren't entirely green mana symbols. Arguably the best card in the deck.

Noteable Exclusions:

Nykthos, Shrine to Nyx - This not making coloured mana on turn one and two is terrible for the deck, to accommodate it, we'd need to play around 24 lands, which would make good Collected Company hits much less likely.

Questing Beast - Four mana doesn't get hit by Collected Company, the card is good, but doesn't do anything dramatically better than the three drops, especially with the printing of Glissa.

Pelt Collector / Experiment One / Avatar of the Resolute - There is a different build of this deck that plays more aggressively, aiming to curve out and get damage in faster. This build is slightly slower, but aiming for each creature to be more impactful than the +1/+1 counter version.

Sideboard Theory: (outdated)

> R/B Midrange:

Their Problem Cards:
Bonecrusher Giant - Stomps our mana dorks when we're on the draw, can trade with most of our creatures.
Graveyard Trespasser - Can trade with most of our creatures when it flips.
Sheoldred, the Apocalypse - Can trade with all of our creatures, deathtouch makes it almost impossible to do better than 1 for 1.
Fatal Push - With Revolt active will kill next to everything in the deck
Extinction Event/Ritual of Soot - Will almost certainly decimate our board, very bad if they land it and we're out of gas.

In:
3x Go for the Throat - Lets us dictate the pace of the game and stops them snowballing value.
3x Garruk's Harbinger - Draws cards and is hexproof, powerful tool.
2x Shapers' Sanctuary - Makes their 1 for 1 removal significantly worse, allows us to keep grinding into late game.

Out:
4x Llanowar Elves - In this removal heavy match elves are less important.
2x Steel Leaf Champion - No value when it dies, evasion isn't too relevant.
2x Yorvo, Lord of Garenbrig - No evasion or value when it dies.

Pressure is the key here. Deny them their 2 for 1s, try to make your own.

> Nykthos Ramp:

Their Problem Cards:
Cavalier of Thorns - A 5/6 will block all of our non-buffed creatures.
Karn, the Great Creator - Enables the combo, can fetch silver bullets like The Mightstone and Weakstone and Cityscape Leveler.

In:
3x Go for the Throat - Removes their creatures if they start to establish board, lets us get through to their planeswalkers.
2x Ghalta, Primal Hunger - When they have next to no removal, this puts immense pressure on them.

Out:
4x Mosswood Dreadknight - Almost nothing in their deck is smaller than a 4/4, trample is nice, but it will never trade.
1x Werewolf Pack Leader - Almost nothing in their deck is smaller than a 4/4, at least this has an ability to be a 5/3.

Opening with an elf is key, especially since we've cut almost all our two drops, don't be afraid to mulligan for a fast opener.

> Gruul Boat

Their Problem Cards:
Bonecrusher Giant - Stomps our mana dorks when we're on the draw, can trade with most of our creatures.
Skysovereign, Consul Flagship - A flying 6/5 is difficult to remove and hard to race, will most likely need to be fought or forced to block.
The Akroan War - Steals our biggest threat and hits us with it.
Obliterating Bolt - Kills half of our creatures.

In:
3x Cankerbloom - Hitting all their big non-creature spells is great, being able to be hit off CoCo is also nice. Can be sacrificed in response to a Stomp so it doesn't resolve.

Out:
2x Mosswood Dreadknight - Can be Stomped if we're not careful, but not a terrible card in the matchup, shaved two.
1x Steel Leaf Champion - Doesn't get any bigger and the evasion doesn't always help.

> Lotus Combo

Their Problem Cards:
Emergent Ultimatum - Tutors for their combo
Languish - Kills almost all of our creatures.
Ritual of Soot - Kills almost all of our creatures

In:
2x Scavenging Ooze - Exile some of their recursion pieces.
2x Ghalta, Primal Hunger - Speed is key

Out
2x Werewolf Pack Leader - A little too slow, hoping not to have to rely on our two drops.
2x Polukranos Reborn - Doesn't put on as much pressure as needed.

No creatures and no removal, a classic combo vs aggro race.

> U/W Control

Their Problem Cards:
Fateful Absence - Efficient removal.
Supreme Verdict - Kills all of our creatures
Farewell - Kills all of our creatures
Aether Gust - Efficient removal.

In:
2x Scavenging Ooze - Exile cards from their graveyard, stop them flashing back Memory Deluge.

Out:
2x Polukranos Reborn - Doesn't give enough value, just a 4/5.

>Mono-White Humans

Their Problem Cards:
Brutal Cathar - Repeatable removal.
Skyclave Apparition - Removes all creatures
Declaration in Stone - Efficient removal.
Destroy Evil - Efficient removal.

In:
3x Go for the Throat - Destroys a Brutal Cathar and gets our creatures back.

Out:
3x Werewolf Pack Leader - Doesn't race quite as hard as we'd like here.

>Abzan Greasefang

Their Problem Cards:
Greasefang, Okiba Boss - Enables their combo, kill on sight.
Abrupt Decay - Efficient removal.

In:
3x Go for the Throat - Removes Greasefang and stops their combo.
2x Scavenging Ooze - Exile Parhelion II and Esika's Chariot, slow them down.

Out:
3x Werewolf Pack Leader - Too slow in this matchup, need more pressure early.
2x Mosswood Dreadknight - A little slow.

>Izzet Phoenix:

Their Problem Cards:
Thing in the Ice - Can force us to return all our creatures to our hand if it flips.
Arclight Phoenix - Recurable flier makes for an inevitable clock
Lightning Axe - Will kill most of our creatures.

In:
2x Scangenging Ooze - Can exile their graveyard and get big enough to survive most removal.
2x Shaper's Sanctuary - Having removal stop being 1 for 1 is huge in this match.
2x Ghalta, Primal Hunger - Damage based removal doesn't deal well with a 12/12

Out:
4x Mosswood Dreadknight - Easiest creature to kill and we don't need the grind value.
2x Llanowar Elves - Die too easily in the removal matchup.

>Five-Colour Fires:

Their Problem Cards:
Fires of Invention - The engine of the deck.
Chained to the Rocks - Cheap removal.
Leyline Binding - Cheap removal.

In:
3x Cankerbloom - Having to lose board presence to slow them down isn't as good as repeatable removal, but in a pinch will save us.

Out:
2x Yorvo, Lord of Garenbrig - Not as valuable as any of the other creatures in the matchup.
1x Steel Leaf Champion - No grind power, which we need here, shaved one.