[Update #2]: MTG Arena's Dominaria United set has now arrived alongside the annual Standard rotation.
[Update]: After a brief round of teasers, all of Dominaria United's cards have now been revealed.
If you're tired of the current Standard meta and you're itching for something new and exciting, you'll be happy to hear that the next big set, Dominaria United, will be launching on September 1st, 2022. It'll bring with it a whole bunch of new cards to play around with, the annual Standard rotation that will see Zendikar Rising, Kaldheim, Strixhaven and Adventures in the Forgotten Realms leave Standard legality, as well as a rather massive escalation in the war against Phyrexia.
What I mean by that last bit, that you can find out in the teaser trailer below featuring one of Magic's oldest planeswalkers - Ajani. Have a gander:
In terms of mechanics, Dominaria United will feature three new and two returning ones to build decks around: Enlist, Read Ahead and Stun Counters, as well as Domain and Kicker. Here's a brief rundown of what each of them does:
Enlist allows an attacking creature to tap down a friendly creature without summoning sickness in order to gain +X/+0 until the end of turn, where X is the power of the enlisted creature. Naturally, since this is a fairly sizable downside, creatures with Enlist will most likely have additional benefits to encourage you to weaken your own defenses.
Read Ahead gives sagas with the keyword the ability to enter the battlefield on whatever chapter you want. Doing so will make you lose out on some value as you will skip the previous chapters entirely, but having the option is certainly welcome.
Stun Counters keep permanents (mostly creatures) from untapping. Basically, if a tapped permanent with a Stun Counter on it would become untapped, instead it stays tapped and you remove a stun counter from it. This seems like a new twist on the fairly old tap-down mechanic, so I expect Stun Counters to play a big role in Limited formats like Draft and Sealed.
Kicker is a returning ability that allows you to pay a bit of extra mana while casting a spell in order to get additional benefits. The only slight difference this time around is that some cards will have multiple kicker costs, thus giving you even more flexibility.
Domain is another returning mechanic that gives you benefits based on the amount of different basic land types you control (Plains, Island, Swamp, Mountain, Forest). The new tri-colored lands from Streets of New Capenna count as three basic land types all on their own, so I expect Domain decks to at least make a bit of a splash in Standard.
As for the cards themselves, you can keep an eye on any of the current and future spoilers over at the official card gallery. Right now the website is slightly out of date as Wizards of the Coast still hasn't updated it with today's (August 18th) previews, but I'm sure those will appear sooner rather than later.
Once the full set gets revealed I'll make sure to let you know. Until then, you can read a little bit more about Magic: The Gathering and its future over at the official website. Enjoy!