The most dominant deck was completely dismantled, and companions are essentially soft-banned with a few exceptions. Welcome to a new era of Standard.
Agent of Treachery and Fires of Invention were a significant factor in accelerating the average turn of the endgame in Standard. Removing them not only decelerates Standard but also cuts off a significant portion of endgame plans decks had access to. "Late game" has recently meant turns 5-7 instead of turns 8+, and these bans open up much more space for traditional endgame strategies like ramp or control.
The companion nerf is nearly a ban of the mechanic itself. Making them cost three extra mana basically rules them out in Standard. Without Fires of Invention to make up for it, Keruga, the Macrosage now not only forces the curve of your deck higher, Keruga, the Macrosage itself costs eight mana to play. Obosh, the Preypiercer forces an awkward, yet aggressive mana curve and now also costs eight mana. Lurrus of the Dream-Den is literally doubled in cost, making it impossible to play Lurrus of the Dream-Den and get immediate use without a lot of setup.
Aggressive companion decks as a whole are essentially dead, with the exception of "freerolling" Jegantha, the Wellspring. Jegantha, the Wellspring is mostly there for when aggressive decks flood anyway, so the cost is less of a deterrent if your deck was already compliant. Linear companion decks are similarly dead. Gyruda, Doom of Depths is a lot less exciting to build around when it costs nine mana to "combo off." Keruga, the Macrosage only really had one deck and Fires of Invention has been banned. Yorion Fires had all of its key components banned or nerfed. The last surviving form of companion deck will likely be a ramp deck with Yorion, Sky Nomad that pays the companion tax early on and then uses Yorion, Sky Nomad to Momentary Blink a bunch of key permanents. Something like Bant Ramp is the natural shell for this, but other color combinations may see play now that it's much harder to cleanly curve Elspeth Conquers Death into Yorion, Sky Nomad.
Don't think this means you've seen the last of the companions though. They're still legal, and many of them are still quite powerful as maindeck inclusions. Lurrus of the Dream-Den has already seen play in Jund Sacrifice, Gyruda, Doom of Depths had several non-companion versions at the start of the format, and Yorion, Sky Nomad is certainly powerful enough to build around.
So where does this leave the Standard metagame? Lukka Fires has been outright removed and many of the aggressive decks have neutered by the change to companions. The format's pillars have been yanked out from underneath… except one.
Temur Reclamation is completely untouched by these changes, and the format is going to start with a heavy skew as a result. Wilderness Reclamation and Uro, Titan of Nature's Wrath are still capable of going over the top of most of the rest of the format, and a lack of companions allows that deck to win via attrition much more often.
The other untouched decks in the format are Jund Sacrifice, Temur Adventure, and Gruul Aggro, with an honorary inclusion of Cycling. All of these decks were reasonable archetypes hanging out just beyond the top tier except Cycling, which was top tier but does lose Lurrus of the Dream-Den. Lurrus of the Dream-Den, however, was not part of the core gameplan and was merely a nice bonus. All of these decks are reasonable starting points, but Jund Sacrifice and Temur Adventure will have to contend with their bad Temur Reclamation matchup.
The first iteration of the winner's metagame will consist of Temur Reclamation, Bant Ramp, and Cycling. These are strong decks with good foundations that naturally push the edges of the format and form the litmus tests of Standard. Beyond that there is potential for decks like Jund Sacrifice and Temur Adventure to adjust and position themselves in that new metagame, with an outside chance for some new decks.
The archetypes most likely to rise up in the wake of these bans are the ones that were held in check by the accelerated endgames made possible by Fires of Invention and Agent of Treachery. Decks like Azorius Control may once again be able to fight evenly through the midgame and establish their own endgame. Mono-Black Devotion may be able to fight on an attrition axis with the dip in companions. My sleeper pick for the new format is a Gyruda, Doom of Depths deck eschewing the restriction in favor of cards like Teferi, Time Raveler, aiming for a slower game with a "combo" finish.
Keep an eye out for the next decks that get to play Teferi, Time Raveler, Deafening Clarion, and/or Lukka, Coppercoat Outcast. They all are powerful cards with a strong play pattern advantage against one of the top three decks I listed. Cutting off instant-speed play, wiping the board early, and jumping to the endgame are some of the strongest things to do in this perceived metagame, and just because Fires of Invention is gone doesn't mean these cards won't have a home. They may even all go in the same deck, though not necessarily.
Lastly, look out for other powerful mana engines that were outclassed by Fires of Invention. Nissa, Who Shakes the World is still legal, Song of Creation may yet have its day in the sun, and Risen Reef is still a powerful engine even in the absence of Agent of Treachery as a top-end. Mana advantage continues to be one of the most efficient ways to win a game of Magic. That doesn't change here.
The only events to pull from this week are LCQs and challenges, but I will still put together a week one metagame breakdown for you all next week. In the meantime: stay safe, stay strong, and take care of each other. Black Lives Matter.