It has been a while since Oran Kremen won Eternal Weekend in North America with B/G Depths. That finish put the deck on the map, and some people—like myself—started toying with the deck.
After a few weeks of testing, I reached a final deck list that I'm happy with:
The deck has just one plan: Make the 20/20 flying avatar. Hence, your matchups are based on your opponent's ability to deal with it. So Delver and B/U/G Shardless are good matchups, and that Death and Taxes and Miracles are slightly unfavorable.
Changes Between My List and Oran's List
Into the North vs. Expedition Map
Playing 3 Into the North and only 6 total snow lands might seem a little odd, but this card is so much better than Sylvan Scrying or Expedition Map when you don’t have Dark Depths that it's worth the risk. Also, this isn't Limited—games aren’t dragging on for long with this deck, and it's rare that you’ll draw your Into the North without targets in the deck.
I found Expedition Map slow and weak to Abrupt Decay; and I liked the sorceries more.
Duress vs. Not of this World
I chose to add an 8th discard spell over Not of this World. While Not of this World protects you against Swords to Plowshares and Karakas, it’s often blank against many archetypes that don’t have ways to deal with the 20/20. So I went for playing only 2 + 1 in the sideboard.
Also, you're always happy to have 1 discard spell in your opening hand, since sometimes your plan is to just see their hand. And, if their hand relies on a fetchland, you can use Lotus Petal or Elvish Spirit Guide to play a Pithing Needle. This strategy is surprisingly effective.
The Tabernacle at Pendrell Vale
I thought this card would be an easy addition, and, since I own it, I was very proud to play this expensive land in my deck. It turns out that it’s not what the deck wants to do, and in all of my matches I never tutored it up even once.
The sideboard contains the most changes. The two most popular decks in Legacy are Miracles and Death and Taxes, and those are slightly unfavorable matchups, which can’t be a good thing. You need to have a sideboard that’s well equipped to bring those matchup into your favor.
Death and Taxes
After some testing, I found that Dread of Night and Toxic Deluge aren’t that effective against mono-white since you don’t care if Mother of Runes, Thalia, Guardian of Thraben, or Flickerwisp die—you only care about their ability to handle the 20/20.
So I decided to try Gloom. If you resolve a fast Gloom, they can still disrupt you with Aether Vial, Karakas, Rishadan Port, and Wasteland, but you have 4 Pithing Needles for this reason. It's strange to say about an aggro deck, but it might be the best card against them.
You still have to be aware of when they have 4 mana up for Swords to Plowshares and Aether Vial to cast their cards, but remember that Vampire Hexmage can remove counters from a permanent—you can target Aether Vial in order to clear the way of Flickerwisps for your 20/20.
The matchup against Miracles depends on how fast you are. There are two versions of Miracles, and you are way better against the non-Legend version. Joe Lossett’s Legend build has Venser, Shaper Savant and Karakas, both of which stop your combo. The "regular" version has only Swords to Plowshares and Terminus.
The fact that you have 3 Pithing Needle in the main is huge, and they are why I love leading with discard spells, because it lets you know exactly what to name.
In the sideboard you have another awkward plan as well: Boseiju, Who Shelters All + Tsunami. This plan is already played in Lands, though the fact that Boil is an instant makes a big difference. In Lands you don’t have Sylvan Scrying though, so we can enact ours more consistently.
Since the pace of the matchup goes rather slowly, I like to board out all 8 Petals and Spirit Guides since you don’t really need to be fast—you just want to have powerful cards.
This matchup is the reason why you have to split your fetchlands if you play Delver. Naming a fetchland with Pithing Needle is a real possibility, but you obviously want to name Wasteland with the first copy.
Stifle is a tricky card. They can’t actually Stone Rain your combo lands with it, if they Stifle the ability of Thespian’s Stage to copy Dark Depths, they’ll just get a one-turn reprieve out of the deal. They can’t Stifle the ability to sacrifice the land and make a 20/20, since it’ll just go on the stack once again because there are 0 counters on the Stage.
You should always sacrifice Dark Depths and get the 20/20 on your turn. If you pass with the combo in play and they draw and play Wasteland, you can’t combo off, and you’ll need time to reassemble the combo.
This matchup is pretty easy. You just have to be aware of Wasteland, Diabolic Edict, and Submerge. This is why I often like to get only one Bayou or Forest and then Crop Rotation it out to play around Submerge.
This is another positive matchup, but you have to be aware that if they have a Baleful Strix, they can block your 20/20 and then make you sacrifice it with Liliana or bounce it with Jace. So you have to play around that with discard and Needles, or with a backup Crop Rotation to get Sejiri Steppe in the case of Jace.
As against Delver, you probably want to make the 20/20 on your turn, but it also depends on whether you know they have Wasteland vs. Liliana in their hand, so once again discard spells are great here.
This deck is fun, and very tricky to play. It might not the best deck in Legacy, but it’s still a solid choice for an open metagame.