- NOTE: Nearly every creature in the deck has a base power of 2 or less, so pretty much all of them will trigger Ezuri, Claw of Progress's effect. Therefore I will not be mentioning this over and over because it will get repetitive.
Elvish Mystic, Fyndhorn Elves and Llanowar Elves are all reliable, cheap, early-game mana dorks.
Birds of Paradise is another cheap mana dork but taps for either of our colors.
Hypnotic Siren at its worst is just a 1/1 with Flying for just the cost of , so it's an easy Exp counter and an evasive creature that can be loaded up with +1/+1 counters for big damage. If we draw it in the early game, we can use it as a beater. However, if we find it in the late game, we can cast it for its Bestow cost and use it to take control an enemy creature. This is a great way to shut down an enemy commander without making it change zones so its owner cannot move it back to their command zone. Hypnotic Siren is just a versatile card in this deck.
Mausoleum Wanderer is cheap to cast, triggers Ezuri and has Flying which gives it decent evasion. Furthermore, it can sac itself to counter an instant or sorcery unless the caster pays , with X being the Wanderer's power. If we put a bunch of +1/+1 counters on it, X is going to be a fairly big number so it'll either counter the spell or force our opponent to pay so much mana to make sure it resolves that they'll be unlikely to have mana for further plays.
Siren Stormtamer is fantastic in this deck because not only does it trigger Ezuri upon ETB, but it has Flying which makes it a prime candidate to buff with +1/+1 counters. And finally, it gives us the option to sacrifice it to counter a spell or ability that targets one of our creatures (or us directly).
Ulvenwald Tracker is a repeatable fight effect that can allow our creatures to deal direct damage to other creatures outside of combat. We're playing a deck designed to buff creatures to monumental proportions so having an on-demand fight effect is a great way to get rid of creatures our opponents are trying to protect. We can't force blocks but we can force fights. Creature removal in Simic is hard to come by so we'll take what we can get.
Gyre Sage can tap for green mana equal to the number of +1/+1 counters on it. With Ezuri, Claw of Progress, we can put all of our experience on Gyre Sage and tap it for massive amounts of mana, great for using on a finisher like Finale of Devastation.
Incubation Druid taps for 1 mana of either Blue or Green (in our deck) but if it has at least 1 +1/+1 counter on it, it produces 3 mana instead. The ceiling is much lower than Gyre Sage but it does at least have a self sufficient way of helping itself out with the Adapt ability.
Sakura-Tribe Elder can sacrifice itself at instant speed to tutor a basic land onto our field. It's a great blocker because we can put it in front of an attacking creature and sac it before damage calculation, thus fizzling the attack and getting a land out of our deck.
Scavenging Ooze is great in here because it gives us an option to disrupt Graveyard based decks such as Muldrotha, the Gravetide, Karador, Ghost Chieftain, Meren of Clan Nel Toth, etc. Furthermore, it synergizes with our +1/+1 counter synergies. Things like Hardened Scales will help the Ooze grow stronger at a faster rate all while we gain life and/or remove important cards from our opponents' graveyards.
Duskshell Crawler triggers Ezuri when it enters and allows us to put a +1/+1 counter on any creature we want. The best part, however, is that it gives each of our creatures with a +1/+1 counter Trample. We want to make sure we're buffing our creatures and attacking for damage; that won't happen if our opponents keep putting chump blockers in front of them. Herald of Secret Streams helps us get around the problem, Skatewing Spy helps us get over the problem, Duskshell Crawler lets us go through the problem.
Invisible Stalker is very difficult for opponents to deal with due to Hexproof. The best part is that it's unblockable, so we can stack a ton of +1/+1 counters on it at the start of combat with Ezuri's effect and swing for massive, unblockable combat damage.
Blighted Agent is another unblockable threat but this one has Infect, meaning it only needs to deal 10 points of damage to a single player to take them out of the game. Not every playgroup will be ok with it, however, so be sure to let them know you are playing it and replace it with another creature before the game starts if they are not ok with Infect.
Thrummingbird lets us Proliferate whenever it deals damage to an opponent, which is pretty much laid out right on the bird's effect text. We choose any permanents with counters on them and give them one more of every kind of counter they have. This can include our creatures with +1/+1 counters, our Simic Ascendancy with Growth counters, our Planeswalkers with Loyalty counters, us with Experience counters and any opponents with Poison counters. That's pretty much everything we should be proliferating whenever we get the chance.
Sage of Hours lets us take an extra turn if we remove at least five +1/+1 counters from it using its effect. If we have at least five Exp counters and Ezuri, Claw of Progress on board, we can essentially take infinite turns by putting counters on the Sage during each combat, not swinging and just removing those counters at instant speed to take an extra turn and repeat.
Benevolent Hydra is a bit like Hardened Scales with extra utility. First off, we can cast it for just which means it will enter the battlefield as a 1/1 which will trigger Ezuri. Or we can sink as much mana into it as we want and make it enter with additional +1/+1 counters. The real value, however, is that it increases the number of +1/+1 counters that would be placed on our creatures by any effect by one. And the hydra itself can redistribute one of its own counters to another creature with its activated ability, so that counter will actually turn into two thanks to its own static effect.
Farhaven Elf lets us find any basic land when it enters the battlefield. Ezuri, Claw of Progress trigger + ramp all in one.
Wood Elves does nearly the same thing as Farhaven Elf except it lets us search for a Forest (which can come into play untapped). This means we can tutor for Breeding Pool and Tangled Islet instead of a normal Forest if we want to. We also have the option of fetching a Dryad Arbor, which is a Forest but also a 1/1 creature, meaning we get another Exp counter if Ezuri is on board.
Champion of Lambholt grows stronger with each creature we play but the great thing is that it makes enemy creatures with lesser power than it unable to block our attacking creatures. If we use Ezuri, Claw of Progress to buff Champion of Lambholt, we can make it insanely powerful without having to wait for it to power up on its own. Then, most of our creatures will be able to attack unimpeded.
Wild Beastmaster is one of our finishers in this deck if the Sage of Hours combo can't be assembled. Whenever she attacks, she gives all of our other creautures +X/+X where X is her power. So we take all of our available +1/+1 counters from Ezuri, Claw of Progress's trigger and stack them on her, turn her sideways and all of our other creatures get the same kind of buff. This, alongside with Cultivator of Blades, is one of the best finishers in the deck.
Rishkar, Peema Renegade can put a +1/+1 counter on up to 2 creatures when it enters the battlefield but the real value is that it turns every creature we control with a +1/+1 counter into a mana dork that taps for green.
Marwyn, the Nurturer is mainly in here to generate massive amounts of mana with her last ability. She can grow stronger herself every time we play an Elf but we can always shortcut by giving her a bunch of +1/+1 counters from Ezuri, Claw of Progress's ability.
Trygon Predator is a repeatable removal option for artifacts and enchantments; all we have to do is deal damage with it to the player with that artifact/enchantment. The nice thing is that it has flying, meaning it's a great target for Ezuri, Claw of Progress buffs.
Cold-Eyed Selkie lets us draw cards equal to the amount of combat damage it does to an enemy player. We have plenty of ways of making things unblockable so it's not unreasonable to expect that this will be drawing us A LOT of cards once it's been buffed by Ezuri, Claw of Progress. Even on its own, it has Islandwalk, so if there is a blue player at the table, be sure to take advantage of that if our hand is running low on cards.
Kodama of the West Tree essentially gives Trample to all of our creatures that have +1/+1 counters, so it acts as another copy of Duskshell Crawler. Furthermore, whenever one of those creatures deals damage to our opponents, we get to ramp which is made incredibly easy because Kodama gives them Trample.
Fathom Mage is an insanely good card draw engine in this deck because it draws us a card for EACH +1/+1 counter that is put on it, even if multiple are placed on it at one time, it still counts each one and draws us a card for each one.
Herald of Secret Streams makes all of our creatures with +1/+1 counters unblockable. Not much to say here, it triggers Ezuri and fascilitates our game plan by allowing our creatures to swing freely.
Skatewing Spy gives each of our creatures with a +1/+1 counter Flying, giving them evasion to help avoid blockers. This sort of functions as a backup Herald of Secret Streams. Remember, we want to go tall and attack to get in big damage. He also has Adapt 2, allowing us to sink mana into him late game to make him even stronger.
Glen Elendra Archmage has insanely good synergy and utility in this deck, let's break it down. First off, it will trigger Ezuri and get us an Exp counter when we play it. After that, we can sacrifice it to counter any non-creature spell. Then, it comes back with Persist, meaning it will trigger Ezuri again and have a -1/-1 counter placed on it which prevents Persist from reviving it again. However, Magic rules state that if a -1/-1 counter and a +1/+1 counter are placed on a creature, they cancel each other out and are both removed from that creature. So if we have a Glen Elendra Archmage that has persisted, we can load it with at least one +1/+1 counter from any number of effects and it essentially deletes that -1/-1 counter, allowing us to counter another non-creature spell and Glen Elendra Archmage will be reanimated due to Persist all over again. Fantastic synergy and repeatable Negates.
Beast Whisperer draws us a card whenever we cast a creature, a useful way of keeping our hand full of gas since we're running so many cheap spells.
Toski, Bearer of Secrets synergizes with Ezuri, has Indestructible making it difficult to get rid of, and draws us a card whenever one of our creatures deals combat damage to somebody. It does everything we want, excellect card for this deck especially considering how many evasive creatures we have that will be connecting with combat damage.
Defiler of Vigor is absolutely insane in any creature-focused green deck, but the fact that it grants +1/+1 counters to our whole team whenever we cast a green permanent makes it that much more ridiculous. If we have any counter stacking effects like Hardened Scales or Branching Evolution, the value is going to be nuts. On top of that, it reduces the casting cost of green spells in exchange for life (definitely-not-phyrexian mana). As if that wasn't enough already, it's a massive 6/6 body with Trample which makes it a great target for Ezuri to buff when combat begins.
Cultivator of Blades has Fabricate 2, meaning we get to create two 1/1 Servo tokens when it enters the battlefield. This means three Ezuri triggers, gaining us three experience counters. The Cultivator's last ability is insanely good in this deck; when it attacks, it gives every other creature a +X/+X buff where X is equal to its power. Normally, 1 power isn't too impressive but remember that Ezuri, Claw of Progress will put a ton of +1/+1 counters on any creature we want as we move to combat, so if we put them all on Cultivator of Blades and attack with it, it'll be giving that same huge buff to all of our other creatures.
Vorinclex, Monstrous Raider has the second half of Doubling Season stapled onto it, doubling the counters we receive along with our permanents. Double the +1/+1 counters, double the Experience counters, double the Growth counters on Simic Ascendancy. Furthermore, it effectively halves the number of counters our opponents put on permanents. Vorinclex himself is an excellent creature to put Ezuri's counters on, because he has Trample and he'll double however many counters would be placed on him. Let's say we have 5 experience counters when we play Vorinclex, Monstrous Raider. We move to combat and Ezuri, Claw of Progress triggers. Normally, we'd place five +1/+1 counters on a creature, but Vorinclex turns that into 10. If we put them on him, we have a 16/16 with Trample and Haste. That's insanely scary and this Praetor can decimate opponents out of nowhere if they don't have an answer for it.