-- LANDS --
Gavony Township - A very synergistic land for its ability to place +1/+1 counters on all creatures I control if you have the spare mana open, which is what I believe to be the primary goal for this deck. You can't proliferate counters if there aren't counters there in the first place, after all.
Grim Backwoods - Having some way to sacrifice your creature(s) in response to a board wipe, spot removal, etc. is basically always a plus, and this land does that. It's just one creature, but getting some sort of advantage back is welcome nonetheless. That said, High Market is better for not requiring mana to activate, but drawing a card is more advantageous than 1 life, especially in EDH. Cards like Ashnod's Altar or Viscera Seer obviously perform this duty better, but then again, they aren't lands.
Reliquary Tower - It's not an uncommon occurrence to have more than 7 cards in your hand, especially if you can stick a Fathom Mage on the board. Unfortunately, a lot of the advantage you build can sometimes go to waste because of your limited hand size. Reliquary Tower is a go-to card for many decks to remedy this issue, since--despite there being several other cards that remove hand size limits--lands are generally the safest permanent types (next to emblems, but they're an outlier).
Woodland Cemetery & Hinterland Harbor - Check lands are good, especially since I don't like expensive fetch-shock/fetch-dual setups in EDH. I keep those in Modern/Legacy where their hyper-efficient mana fixing abilities are more aptly used, especially on a limited budget.
Yavimaya Coast - I'm a huge fan of pain lands in EDH, since they enter untapped and fix mana for just a ping, which is much more manageable in a 40-life format and you won't always need their colored mana anyway.
Temple of Mystery - The temples/scry lands are slower lands as they must enter tapped, but fixing a draw is nice. I chose Mystery specifically because I feel green and blue are the most needed colors in this deck, especially together (there's a lot of Simic cards in this list). With the tri lands, bounce lands, Murmuring Bosk, and this land, there are a total of 7 lands in this deck that must enter tapped.
Mirrodin's Core & Gemstone Mine - Lands that tap for any color are obviously the most desirable in EDH, especially in 4- or 5-color decks. These two do that while being thematically appropriate and synergistic with Proliferate, much like the included Storage Land, Dreadship Reef.
-- ARTIFACTS --
Everflowing Chalice - The colorless counterpart to Astral Cornucopia, basically. It's at least usable in most EDH decks, but Proliferate effects clearly make this card an ace mana rock.
Chromatic Lantern - I'm sure we all wished they had included one of these in all of the pre-cons instead of just Yidris's, but oh well. For newer players reading, just keep in mind that this card's utility and power increases exponentially with the number of colors in your commander's color identity, so the only decks in which this card is more necessary are 5-color.
Gemstone Array - It's similar to a non-creature version of Crystalline Crawler, but it can't tap to put counters on; rather, it requires an initial investment to generate its counters. That said, untapped land can be kept up between turns for abilities/instants/mind games then tapped just before your turn to net gain mana. Likewise, being fully tapped out doesn't mean an inability to cast spells or activate abilities as long as there are counters on this card.
Umezawa's Jitte - A legendary (literally and figuratively) equipment for several reasons. Its inclusion as the only equipment in the deck is to help Atraxa push for possible commander damage wins while also being an equipment to utilize charge counters for that added thematic flavor.
Bow of Nylea - The part of its casting cost is irksome sometimes, but it's another way to put +1/+1 counters on your creatures, among other possible modes (they're small effects, but nonetheless welcome). Worth mentioning is that you can place the +1/+1 counters on any creature on the board, not just your own; especially with Proliferate, you can make some neat political moves with the ability to buff other players' creatures. Also, worth noting is the interaction with Bramblewood Paragon: if your creatures have Trample and Deathtouch, you can assign one damage to a blocking creature and the rest to the defending player. It's not quite as good as unblockable/Horsemanship/etc., but still nice.
Ring of Three Wishes - An all-star in this deck, since you'll be able to Proliferate the wish counters and tutor for a card every turn. It's a pretty good card in any deck (especially since it's a colorless tutoring card), but it pulls extra weight here.
-- PLANESWALKERS --
*note: planeswalkers in general are going to be more powerful in a deck like this than most because you can accelerate to their ultimate abilities more quickly. In fact, many other Atraxa lists go full Superfriends and focus their core strategy on them.
Jace, Architect of Thought - All of his abilities are relevant in EDH: his +1 pads your life and can protect your creatures, his -2 helps dig through your deck, and his ultimate is incredibly fun and will have different powerful effects from game to game.
Liliana Vess - Classic Lili's ultimate is, word-for-word, the original Rise of the Dark Realms, but her -2 is the main reason behind her inclusion. Having a repeatable Vampiric Tutor without the life cost is a very welcome contribution.
Garruk, Caller of Beasts - The potential advantage you can build from this walker is quite scary. Digging into your creatures, cheating creatures into play, and an emblem that turns every creature into a super-tutor is insane.
Ajani, Mentor of Heroes - He either digs for more creatures/walkers or puts +1/+1 counters on creatures, two very relevant abilities in this deck as I've previously outlined. It's also not entirely uncommon to get to use his ultimate and gain 100 life since both of his other abilities are plus abilities.
-- ENCHANTMENTS --
Inexorable Tide - One of the most obvious includes in the deck, and probably one of the first cards many people add or seek to add to their Atraxa lists. Adding Proliferate to every other spell you cast can get out of hand very quickly for your opponents.
-- INSTANTS/SORCERIES --
Mystical Tutor & Worldly Tutor - Cheap tutors are always welcome in EDH.
Swords to Plowshares - One of the best spot removal cards available.
Traverse the Ulvenwald - This card is either a cheap and effective pseudo-ramp spell or, if Delirium is activated, an amazing tutor card, making it relevant early- and late-game.
Regrowth - Another card added to interact with the graveyard, and an all-star green card regardless.
Otherworldly Journey - A cheap and flexible card, allowing the reuse of ETB effects, the removal of an attacking creature from combat, or the dodging of a targeted hate spell in addition to adding a +1/+1 counter.
card:Give//Take - Two very valid effects on a Fuse card is welcome, and either (or both) are used depending on what is needed: counters or stuff to do with counters. This deck struggles with card draw if you can't stick Fathom Mage (or the not-as-powerful Zameck Guildmage or Sage of Fables), so this card can smooth that ailment out.
Wargate - Because of its Bant-colored requirements, it's only usable in a limited number of decks, but it's a very powerful card in the decks it can be played. It's very flexible, fetching for whatever is needed; also, x=0 can fetch a land (usually Golgari Rot Farm or Azorius Chancery) to ramp if necessary.
Divine Reckoning - This card replaces Duneblast from the pre-con. At least one wrath effect is necessary in basically every deck, even aggro-centric decks as a Plan B; that said, having two wraths in one card slot is great even if it's a less-than-optimal wrath. I particularly like it since you can trim the board of excessive threats while keeping Atraxa in play to keep Proliferating.
Unburial Rites - One of my favorite reanimation spells because it can be used twice on its own. Combined with cards like Regrowth to get it back from your yard, you can keep reanimating over and over again.
Increasing Ambition - Five mana to tutor is below average (assuming Diabolic Tutor to be average for tutor effects), but effectively being able to turn one card into three between it's initial cast and using its Flashback is very efficient.
-- CREATURES --
Zameck Guildmage - The Ravnican guildmages are notable for being bears with (generally) useful abilities, and Zameck fits that description well. It either puts +1/+1 counters on creatures if the spare mana is available, or it turns +1/+1 counters in more cards. It's synergistic with itself (which is awesome card design IMO) and with the rest of the deck.
Bramblewood Paragon - Replaces Tuskguard Captain from the pre-con. She's one mana cheaper than the Captain while offering the same evasion. Ultimately, both work, but the Paragon is cheaper in exchange for not having Outlast (which is too slow for me). It's worth noting that her first ability works only with Champion of Lambholt in this list.
Wood Elves - I run two less lands than the pre-con (from 39 to 37), but Wood Elves is particularly nice since it a creature that ramps (it can fetch for Murmuring Bosk!) and can be a relevant threat with enough +1/+1 counters, as any creature can be.
Sage of Fables - There are a few Wizards that benefit from its first ability, but the ability to turn extra mana and counters into card draw is incredibly welcome. It's welcome redundancy with Zameck Guildmage's second ability, but has the added benefit of being instead of .
Edric, Spymaster of Trest - Edric replaces Bred for the Hunt from the pre-con. It basically has the same effect without the added hurdle to jump over while also being a huge political card. Edric encourages opponents to swing, but it also encourages them to swing at anyone but you. In addition to this, Edric is simply a creature that can hold +1/+1 counters, while Bred for the Hunt is not.
Altered Ego - Copy effects are always fun and potentially very powerful, so having what is basically a theme-appropriate version of card:Clone(M12) is a great.
Heliod, God of the Sun - Heliod replaces Brave the Sands from the pre-con. It cost two more mana, but it can be an indestructible creature that still gives Vigilance to the other creatures. Also, it can create more creatures if there aren't other uses for mana (again, great with Cathars' Crusade).
Duskmantle Seer - It's not a deck of mine if it doesn't have Duskmantle Seer. Being a 4-mana 4/4 flier is quite nice on its own (making +1/+1 counters on him quite scary), but being a Dark Confidant for everyone can really accelerate a game. What's really fun is making copies of him and having two or more triggers of his ability.
The Mimeoplasm - A creature that takes the best abilities and highest powers currently present in a game and staples them together? Sounds great. Furthermore, that power boost comes in the form of +1/+1 counters, offering synergy, graveyard relevance, and power all in one card.
Sire of Stagnation - I like to call this card the "Poor Man's Consecrated Sphinx." It's obviously not on the same level, but it can definitely get out of control very quickly. It directs a lot of hate towards it, but nonetheless it's a powerful card.
Avenger of Zendikar - Just about any green deck can benefit from playing Avenger, but it's especially powerful in a deck like this that can really take the Plant token army through the roof very quickly with Proliferate, Cathars' Crusade, Master Biomancer, etc.
Mikaeus, the Lunarch - One of two X-costed creatures in the deck, and a very synergistic and powerful one at that. While he doesn't play well with reanimation abilities (without cards like Cathars' Crusade, anyway), The ability to add +1/+1 counters on all of your creatures is, as mentioned many times before, the primary goal of this deck. Additionally awesome is the fact that he basically does this for free if he is Proliferated.
Hangarback Walker - The other of the two X-costed creatures. In this deck, Hangarback is usually what I call a "Wrath Insurance Policy," in that you're left with creatures should you be wrathed while he's on the board. His synergy with Cathars' Crusade/Master Biomancer is understandably insane. Not much else needs to be said; he's a big dude who gets bigger and pops into a bunch of smaller dudes, what's not to like?
, +1 Sorin, Solemn Visitor, +1 Elspeth, Sun's Champion