In all my long years cubing I have never been able to get an aggressive green deck to be viable. It simply had nothing over the red or white aggressive builds that come with the removal that green sorely lacks. Ramp, what green gets instead of removal, is all well and good but it tended to just exacerbate your other pre existing weaknesses. Curving with ramp, while powerful, is harder to do than conventional curving as you need more things to line up for you. It also makes you more vulnerable to removal and to drawing dead cards in the mid and late game. Historically the best aggro green builds have been those that just go with threats from the outset and forgo mana elves. Or indeed just being an elf deck and becoming more combo than aggro, but at least good! Not playing one mana ramp is forgoing green's greatest strength for no real advantage over other colours.
So what has changed? Why is green now packing aggro decks that are top tier? It is the result of a culmination of multiple factors over a few years. Things began to pickup for green around Kaladesh and has recently hit a threshold of cards and effects that has made aggro green a consistently top tier build in my cube.
Not only has the card pool and range of what cards do increased over time but the meta also evolves. A big factor in aggro green improving is that tempo has become more important over the years. With tempo being more valuable the benefits of ramp have increased. This is paired up really nicely with the ability for green decks to obtain card advantage in a wide array of places, usually at little to no tempo cost. It means that you can easy avoid the pitfalls of playing ramp with card advantage tools and still reap the huge tempo perks. Indeed this ability to pair ramp along with high tempo card advantage has given aggro green a very serious play style that is essentially just brute forcing a win. A lot of powerful green cards provide a mana boost even as you go higher up the curve from a selection of planeswalkers to cards like Primeval Titan, Old-Growth Troll, and the Great Henge. Plenty of other green cards are also helping you to make land drops rather more consistently than other aggressive lists too, be they finding you lands or letting you play them off the top. All told, green winds up with a good amount of mana that tends to continue growing as the game goes long. Paired with good card advantage and things can spiral in some pretty extreme ways. You can face some pretty scary things and instead of dealing with them you can just totally overwhelm them by playing two or three times as much stuff as your opponent every turn. This is typically a means of reach and is something green very much has over white aggro decks. I have come close to decking myself like this on numerous occasions!
It is not just card advantage helping out here but also card quality. Green has the best non-blue card quality effects in Oath of Nissa, Once Upon a Time and Abundant Harvest, not to mention looting from Smuggler's Copter. As card quality effects are generally a tempo cost they are not something aggro decks are looking to pack much of. They do however make for exceptional filler in all the possible ways. They sort out curves, they add to your count of playables, they sort out mana ratios. If you have a hole in your deck a card quality spell is there to plug it up. Much as we might look at the big names at the top of the power scale to see why an archetype is getting better it is just as important to look at the bottom end of the power scale too. What is happening when you miss the mark in the draft? The answer is becoming that you suffer less if you are green. There is enough one mana ramp to go round so rather than winding up with little to none and an unplayable deck you will just have some of the less powerful or suitable options in your one mana ramp slots and a deck that remains functional. The existence of good card quality along with decent filler cards like Elvish Visionary, Llanowar Visionary, good MDFC lands, along with a bunch of generally fine-to-throw-in-most-decks midrange cards like Courser of Kruphix, and you find that green has a very high floor. A good curve with a bunch of random good green cube cards and you tend to have a fairly functional pile. This is part of what makes red so good presently. It just doesn't seem to matter much how you mix your red cards beyond curve, you just wind up with something competitive. Green seems to be catching up to red in that regard.
The next big change is the nature of the threats now available to green. Historically it was mostly just big dumb dorks. Sometimes it was little dumb dorks but whatever it was it was held off comfortably with your standard anti-beatdown plans. Spot and mass removal always seems overly effective against green aggression. The two main ways green threats have evolved is in diversity and immediate effect. Green has more creature lands, more vehicles, more top tier planeswalkers, and more robust and unusual dorks than ever before, and many at high power levels. Lair of the Hydra, Smugglers Copter again, Toski, Nissa Who Shakes the World, Hex Drinker, Old Growth Troll, Esika's Chariot etc. These cards all tax answers while being able to apply good pressure. The quantity and high power level of cards like this has helped push green a lot in recent years.
The second class of improved threats, the immediate effect ones, comes in two guises - those that kill stuff, and those with haste. Green still isn't great at killing things and doesn't really plan to when going aggro. It aims to simply over power anything it faces with bigger and better threats alongside more cards to play and more mana to ply them with. Even so, removal that doesn't cost you power is worth playing. Voracious Hydra is the best in this regard although some older classics are still a nice support such as Jitte and Garruk Relentless. Walking Ballista is also at it's best in the aggro green with good mana production and often some +1/+1 counter synergies. I have even seen Ugin the Ineffable getting a bunch of play in these aggro green lists. That is another perk of the archetype - being able to hit your land drops and consistently ramp means you are packing five and six drops without any cost where other aggro decks are having to make build adjustments to sensibly include that level of top end. Ideally my red and white aggro decks are not playing any five or six drops at all.
So, to the big one. Haste dorks. This is the single biggest contributor to the overall improvement of green and it is mostly down to a fairly small number of cards. Haste is just so good at the moment. It gives you a really reliable means to secure some value from your threats, be that applying a lot of damage or planeswalker control. It also forces opponents to play with a much higher degree of respect for what you can do. With no haste dorks at all your opponent can feel really safe with sorcery removal. A Wrath will make them feel immortal! If they can clear or stall the board they can lay walkers with complete confidence and start to lock down the game. Haste is the EtB "value trigger" that aggro decks most want from their dorks as it giving you the outcome directly that you are investing your resources into doing! In essence it is like comparing Cavalier of Gales and Thundermaw Hellkite. Both are five mana 5/5 fliers but one Brainstorms for value on the turn you make it while the other does a Lava Axe! Which is better depends on what you are trying to do. In the case of the aggro green deck haste is the kind of value we like most in our bigger threats. As a direct source of card security and on-theme value, as a means of keeping our opponents in fear of what we can do, and as a means of just beating the crap out of unsuspecting people as quickly as possible! Questing Beast and Vorinclex are two newish powerhouses that have really helped green perform in this area. Both are really scary to face and as an opponent of green you are often just praying they don't have one. Vorinclex isn't only a juicy hasting threat, he is also quite a savage disruption tool that negates a lot of cards. Getting a bit of free disruption on your threats is always nice for the aggro player and not something green has previously had the chance to enjoy beyond some mild graveyard removal stuff. Speaking of which, Froghemoth, while not at the same level as the hasting legends, is still an impressive tool in the aggro green players arsenal. There are a number of land converting walkers that are pseudo-haste threats. Shifting Ceratops, Vengevine and Surrak are also all fine green dorks with haste that support the aggressive strategy nicely. I haven't even been running those final three four drop dorks in my cube lately and aggro green is still performing admirably.
Lastly I would say that green has gained some agency in recent years. Historically playing the archetype was rarely more than a case of curving and turning sideways. Sometimes you had to consider Wraths and sometimes you have to work out the correct attack but it was linear and low option density. Now we have not just card quality but also things like MDFCs, modal cards, Ranger Class, and just a lot more ways to use your cards. A number of good green cards have mana sinks on them as green likes such things. Mana sinks don't just give you an option in the late game when everything else has run out, they also give you options in the midgame too. Options don't have to be more powerful uses of mana to be situationally more powerful things to do. Animating a manland so as to kill of a planeswalker is going to generally be superior to playing something out from your hand for example. Green tends to have more of these low power options and so more often finds itself in a position where using them is the best line even in the midgame. Gaining agency is huge, it makes you far less of a whipping boy to control players and is makes games way more interesting and involved. You feel like you won the game rather than the deck and good RNG winning the game.
Combat Tricks have gotten better recently too with Snakeskin Veil, Blossoming Defence, Wild Shape, Inscription of Abundance, and Vastwood Fortifications all being new and all being comfortably top ten cube combat tricks. They are cheap, often useful in multiple ways, often as a trick or as protection, or they are useful in an ongoing way such as a lasting buff. Mutagenic Growth remains my top pick combat trick but by far and away the best thing it does is save your mana dorks from getting Shocked it seems. Much as I quite like running a combat trick in my aggro green decks they really don't need them. You certainly don't want loads of them. They are great now and again but often sit about making you wish they were a land or proactive play. The best thing they do is put the fear into your opponent. Combat tricks will reduce the consistency of your deck and are a bit of a high roll card. I will only be playing them when my deck is so well tuned that I can afford to run them or such a train wreck that I need more playables and/or that ability to get lucky and have more than my fair share of high roll moments.
You will note I have talked a bunch about Smugglers Copter, Umezawa's Jitte and Walking Ballista a fair degree in this article. These are all quite high pick cards in draft as they are pretty powerful, pretty playable, and let you remain more open. These are certainly some of the mostly highly picked cards early in a draft. They all not only go in aggro green decks but are also basically at their best in that archetype as well. These cards not only make the archetype better for one reason or another, they also push you in that direction somewhat and result in it getting more play. Each of these cards fires on multiple positive synergies for mono green. Ballista and Jitte both give removal options. Copter and Jitte both put small chaffy dorks to good use. Ballisa and Jitte to some degree are good mana sinks. Copter lets you access the world of fliers. Ballista loves a +1/+1 counter effect etc etc. This general suitability for a lot of the colourless cards has allowed for aggro green to be a solid home for Urza's Saga and Karn Scion of Urza. In my very last cube I got battered by Esika's Chariot copying construct tokens. While not the easiest to piece together a construct build is certainly impressively powerful. There is a lot more subtle support for such things kicking around than you might expect. A simple Tireless Tracker can turn your constructs into monsters!
In a similar vein to working well with colourless stuff green is also the best colour to splash with. It has the best fixing in every aspect and can make a splash work easily most of the time. You don't need to splash and probably don't want to unless the colour pair is open and you are tabling all the fixing and gold cards. Or you train wreck and need the help! It does however give you access to more picks as well as powerful and complementary cards. Grist has become a pretty common splash. Kessig-Wolf Run historically is the most common thing for green decks to splash for. Removal effects, powerful gold cards, and un-green like dorks, typically fliers like Emissary of Grudges, Restoration Angel, and Hydriod Krasis are the sorts of thing you see getting incorporated into aggressive green decks.
Here is a quick and no frills example list of how you might build this deck. Loads of the parts are interchangeable and there are plenty of worthy inclusions that I didn't have room to showcase in this list or the following one. The bombs you really want in the archetype are Questing Beast and Esika's Chariot. Beyond that it is about getting the right curve and ratios more than it is about specific cards. You can do without specific things, no card is key to the archetype. You do want some one mana ramp but it isn't critical which. Even the likes of the Great Henge is pretty much a luxury card, a bit on the win more side. It is one of the few things on this list you could cut and replace with a card baring no curve or function similarity. You might also note that were are able to get rather more utility in our mana base than other archetypes. This is thanks to our reasonable ability to have lands and mana. The higher curve likes access to a healthy land count and the expected extra card draw allows for a bit more spice within those lands.
Werewolf Pack Leader
Toski, Bearer of Secrets
Nissa, Who Shakes the World
Vorinclex, Monstrous Raider
The Great Henge
15 (17) Lands
Lair of the Hydra
And here is a quick example list of the Saga green deck that smashed everyone up in my last draft;
23 (24) Spells
Once Upon a Time
Bala Ged Recovery
Augur of Autumn
Karn, Scion of Urza
The Immortal Sun
16 (17) Lands
Lair of the Hydra