We now know the newest Buy-a-Box Promo, the new largest black bordered creature in Magic.
There's always been a special honor to being the biggest creature, no matter how bad the biggest creature was at the time. The biggest numbers available in Magic have now officially doubled since Alpha, when Force of Nature reigned supreme. This removes the mantle from Emrakul, the Aeons Torn as we inch toward a natural 20/20.
We had to know Emrakul wouldn't be the biggest forever, but it was cool that, for a surprisingly long time, honestly, the biggest creature was also the most powerful to put onto the battlefield and a truly epic part of the story, but everything in Magic changes, and now that special honor is held by Impervious Greatwurm.
Buy-a-Box promos are still new, and we're still figuring out exactly what kinds of cards to expect and Wizards of the Coast is figuring out the best kinds of cards to print.
They've painted themselves into a tricky corner. It's important for Magic's economy that these cards are desirable because they're a tool WotC is using to support brick and mortar stores, which are an important part of Magic's infrastructure because they offer a place for people to meet and play in person that online retailers and big box stores don't offer. So these cards really have to matter.
At the same time, for now, they've decided that part of making them matter is making them uniquely available through this promotion and making them foil, which means the card only exists in foil, which can be a problem for tournament players, especially in humid regions where foils often warp.
The other issue is that WotC has decided to make them Standard legal. This means that if the card is powerful, it will show up in Standard decks, which will force people to play with foils. A solution is to print cards at a power level such that they won't show up in Standard decks, but that creates an interesting puzzle. How do you make a card that players want that isn't good enough for Standard?
The first attempt we saw was Firesong and Sunspeaker, a card that was clearly designed for Brawl and Commander. This is a natural fit for the card, and something players expected to continue. The Buy-a-Box promo would be expected to be a card designed for singleton formats. Nexus of Fate showed that we can't expect that, and it was met with mixed reactions.
Now, we have a creature that will be desirable to some players just because some players always want the biggest creature. Honestly, I think that's a good solution: flashy enough to hold some value, but a card that won't be a major player in Standard. It's regrettable that Emrakul's time at the top had to come to an end, but we knew this was coming.
The question is what it means for future buy-a-box promos. There aren't a lot of analogues to this, and they certainly can't just make a 17/17 next set (right...?) For now, that's just a problem for WotC.
For most of us, the most important immediate takeaway is that we can expect that convoke is back as the Selesnya mechanic in Guilds of Ravnica . If the mana and surrounding card pool push Goblin Chainwhirler out of the format, that could be a big change for which green and white cards are good moving forward. More speculative players might want to start taking an interest in cards like Legion's Landing that are extremely powerful when you want a lot of creatures--if one toughness isn't a huge liability. Similarly, it might be a good idea to pull Saproling Migration out of the bulk and into the playable commons box if you organize your cards that way.
At the same time, convoke is a mechanic you need to be really careful with. I think it was too pushed in M14 Limited, which was largely defined by Triplicate Spirits, and there have only been a few convoke cards that really mattered in Constructed (off the top of my head, I'm thinking of Chord of Calling and Stoke the Flames, and obviously, we won't see something like Stoke the Flames in Selesnya). It's tricky to balance convoke because it's so much better in Limited, where there are usually creatures on both sides of the table, than in Constructed, where overextending as a core strategy can be a huge liability. So we may or may not see convoke actually shape Standard.
The other question is what this implies about other returning mechanics from Ravnica: City of Guilds. Personally, I really doubt WotC would lock themselves into reusing all ten original guild mechanics, and undoubtedly some are seen as successes and others as failures. And besides, can you really imagine them reprinting haunt? (In before I look really stupid.) I imagine this means we'll see a balanced mix, reusing mechanics where they can to try to get a roughly even split of old and new.
As for Impervious Greatwurm itself, what are we working with? Does this have any utility?
Conceptually, there's something to be said for a big indestructible creature as a payoff for a go-wide strategy, in that most sweepers won't kill a big indestructible creature, so you've added to your battlefield but diversified your threat portfolio, as it were.
On the other hand, if you're trying to cast this on turn 5, let's say, that means you need to have untapped with five creatures on the battlefield and played your fifth land on turn 5, or untapped with six creatures and only four lands. Rather than attacking with those creatures, you tap them to play another threat. Why, in this scenario, is a big creature better than an anthem or overrun effect?
Look, if I had a good answer to that question, I wouldn't have lead off with the understanding that this card just won't be much of a factor in Standard.
The other problem, beyond "why do we care about making this big threat when we already have a battlefield" is "Why is this the threat we want?" How good is a 16/16 indestructible? There are so many creatures in Standard right now that resist dying: indestructible Gods, Rekindling Phoenix, and eternalize creatures, for example, that players don't lean heavily on "destroy" effects, instead putting a heavy premium on exiling. Many of those threats will be rotating out, but the removal suite available in Standard will still include Settle the Wreckage, Vraska's Contempt, Doomfall, and Ixalan's Binding, just as some examples. And, of course, with no evasion, it's not clear the opponent even realistically needs to answer it. Ghalta, Primal Hunger frequently attacks into large battlefields and demands that the opponent chump block with several creatures before dying the following turn. The payoff for Impervious Greatwurm is often far less threatening.
You might be more interested in a large creature than an anthem if your opponent has a high enough life total that a mass pump effect won't make your 4-6 1/1s lethal, like, if your opponent started with more than twenty life, but I still doubt this will be the threat you want in any but the most casual Commander settings. It has some chance in Brawl, just because there's a lot less competition for this kind of card, and the singleton format might mean you're in the market for an extra, weaker Ghalta.
More likely, if you're thinking about this card, you're interested in it just for its printed power and the rules text is meaningless. As I remember, when Krosan Cloudscraper was the biggest creature, it was used in conjunction with Sutured Ghoul on occasion just to exile to make the Ghoul big enough to be lethal in a single attack. Unlike Emrakul, the Aeon's Torn, Impervious Greatwurm can hang out in a graveyard without issue, which allows it to be used for things that care about its base stats like The Mimeoplasm, in fact, I wouldn't be surprised if a large portion of the time this card is played, it's played in decks where The Mimeoplasm is the commander, because this is the best creature you can exile to add counters to the Mimeoplasm, and that's one of the cleaner concrete things that this card is the absolute best in the game at.
No matter how bad a card is, if it's the best at something, it'll find a home. For now, Impervious Greatwurm is the best at printed power and toughness, and there are certainly other cards that are also just looking to check that value.
What this means is that, contrary to a first reading of this card, the best Impervious Greatwurm decks are extremely unlikely to care that this card has convoke. Indestructible is also basically flavor text.
While it has a lot of power and some of the competition doesn't stay in a graveyard, this is unlikely to be a desirable reanimation target since it doesn't have evasion or any useful abilities, and it's too expensive to use with something like Pandemonium or Varolz, the Scar-Striped. It has to work with cards that are literally only concerned with the printed stats, like The Mimeoplasm and Sutured Ghoul; I believe there are likely other cards, but they're not coming to mind and I can't think of a useful search term in Gatherer.
Ultimately, people will complain about this card because they'll end up owning it even though it's not for them. A lot of casual products these days go straight into the hands of casual players exclusively, because they're sold in Commander products that most competitive players don't buy. Competitive players do buy boxes, so they'll end up owning Impervious Greatwurm and it won't look useful to them. That doesn't mean the card has no purpose and it doesn't mean printing it was a mistake.
Any card with unique utility has a purpose somewhere, and you don't even have to look that hard to find a purpose for the biggest creature. As to whether it's a mistake, I ultimately think the current set of conditions guiding Buy-a-Box promos is unsustainable. It's too hard to make something desirable but not for Standard because it only exists in foil, but also Standard legal. I think something has to give. The promo needs to stop being foil, non-foils need to be available somehow, the card needs to not be legal in Standard, or something like that, but while all those restrictions exist, I actually think this was a reasonably safe and clever solution to a difficult problem, and I think it will have and hold more value than Firesong and Sunspeaker.
One of the biggest points that will inform what direction these cards take, I expect, is the success of Brawl. The card pool in Commander is so large that it's really hard to make a card that will really see play in Commander but that isn't good enough for Standard, even targeting the format specifically without being as heavy handed as something like Command Tower. I suspect that WotC's hope is that Brawl is popular enough that they can design these cards specifically with Brawl in mind and that that will lend them enough value that people care about getting the promos. Personally, the move to a lower life total in two player Brawl games took a bit of the wind out of my sails on the format, but I'm not sure how well it's doing with other players, and it's okay that a change was made that didn't appeal to me personally.