Merfolk Branchwalker is not a good Magic card.
Brad was right.
However, since the rotation of Kaladesh it was been the only reasonable option as far as green two-drops are concerned. But a certain Elf Crab Mutant is about to change all of that. Enter Growth-Chamber Guardian.
Growth-Chamber Guardian provides a medium body in the early game combined with a steady stream of value. It's not incredibly large for its mana cost, but midrange creature decks generally prefer grindy long-term advantage to immediate impact. Growth-Chamber Guardian amplifies to become a 4/4 which is an important breakpoint: large enough to attack into a Crackling Drake or Goblin Chainwhirler and to block an Adanto Vanguard all day.
I think it's fairly likely that Golgari Midrange will end up playing Growth-Chamber Guardian. While there's no guarantee that Golgari Midrange will remain a top tier deck, I think it's more likely than not that it survives in some form.
Growth-Chamber Guardian vs. Wildgrowth Walker
The single factor that could keep Growth-Chamber Guardian from seeing play in Golgari Midrange is Wildgrowth Walker. Walker is a plan in and of itself against aggro decks and forces Golgari players to run large numbers of the mediocre Merfolk Branchwalker, even if Growth-Chamber Guardian is better in a vacuum. Since Growth-Chamber Guardian almost demands deckbuilders play the full four copies and both cards are green two-drops, I think playing Wildgrowth Walker implies excluding Guardian and vice versa.
Luckily, I think new Standard will cause Wildgrowth Walker to gradually leave decklists anyway. The problem is this: Mono-color decks aren't getting many new toys. Wildgrowth Walker primarily exists as an answer to Boros Aggro and Mono-Red Aggro. Those two decks, with their nearly mono-colored manabases, do not benefit much from the powerful gold cards Ravnica Allegiance brings to the table. While Boros could splash a color other than red to get access to a few of the new cards, I doubt that it would improve the deck very much.
With every other deck getting stronger, I expect Boros Aggro and Mono-Red to fall in metagame share - standing still while others move forward is never a good place to be in Magic.
At the same time, the currently previewed cards suggest that the newer aggressive guilds tend more towards midrange.
Bedevil's restrictive mana cost and inability to go to the face make it a poor fit for most aggressive decks, while many of Gruul's best cards cost three or greater mana, rather than the one or two mana cards that all-in aggro decks thrive upon. That means that even if Rakdos and Gruul break into Standard, I doubt it will be in the sort of shell Wildgrowth Walker shines against.
Beating Control with Growth-Chamber Guardian
In the slower, more controlling metagame I'm predicting, Growth-Chamber Guardian is perfect. Its ability activates soon enough to guarantee value before Kaya's Wrath. This is critical given that the card will almost inevitably be the backbone of Esper Control. Against Deafening Clarion, it's even better: it ignores the sweeper on the play. On the draw, it will most often trade one-for-one with Clarion while generating a small mana advantage.
In addition, the ability to generate value without casting spells against control is invaluable. When the blue control player holds up a counterspell, you can activate the Guardian to make tangible progress while wasting their mana. This, in turn, forces them to tap out, which allows you to resolve your best spells at a higher rate.
Growth-Chamber Guardian is also an excellent bait spell. If it resolves, you can activate it immediately rather than providing them a target for their counterspell. It if doesn't, it only costs two mana, so it's easy to follow-up with a more expensive threat. The cheap mana cost also makes it easy to resolve Growth-Chamber Guardian through Quench, our new Mana Leak replacement. Guardian will also allow you to play around Quench with your other cards without wasting that mana.
Growth-Chamber Guardian makes cards like Seal Away and Settle the Wreckage extremely awkward. No one wants to spend a removal spell on a creature that has already found another copy of itself, but the fact that these spells only work during the attack step makes that an inevitability. The icing on the cake is that adapt is instant speed. It's easy to leave up Vraska's Contempt for a Teferi or Niv-Mizzet with Growth-Chamber Guardian around.
If the metagame does move towards slow, grindy decks, here's what I think Golgari Midrange might look like:
- 3 Carnage Tyrant
- 4 Druid of the Cowl
- 4 Growth-Chamber Guardian
- 4 Jadelight Ranger
- 4 Llanowar Elves
- 2 Midnight Reaper
- 3 Ravenous Chupacabra
With Growth-Chamber Guardian acting as a mana sink and less need for Merfolk Branchwalker, this list can find room for the full eight mana-creatures. That allows it to play many copies of Karn, Scion of Urza and cast it on turn 3 with startling consistency.
Turn 3 Karn: Good in all formats!
Karn also allows the deck to make excellent use of Treasure Map out of the sideboard, a card that has already proven itself a powerful weapon in Jeskai Control. Karn and Treasure Map are both powerful grindy cards, well-suited to the world where Guardian ends up being maindeckable.
Ultimately, predicting the metagame of a format that doesn't yet exist is an incredibly difficult task. At this point, with so much yet to be previewed and so few games of the new format played, everything is uncertain. What I describe here is one path Standard might go down and how to exploit that path. If everyone continues to play aggro decks in large numbers, Growth-Chamber Guardian might never make a splash. But a month from now, you might start to notice aggro decks slowly being replaced by control decks at the top tables. If that happens, and Golgari Midrange still exists, then you'll know that it's time to keep the growth-chambers safe.