https://magic.wizards.com/en/news/mtg-arena/mtg-arena-announcements-august-12-2024
Catch up with the latest info and events on MTG Arena.
In this edition:
Based on the timing and the unpronounceable name, the Midweek Magic event scheduled for the first week in September is likely to be similar to last year's "Yargle Day" event.
They've updated the Midweek Magic page now and it's not that similar:
Choose any legendary Frog (or Tatsunari, Toad Rider) on MTG Arena and build a Brawl deck without needing the cards in your collection! Plus, Yargle's magic makes all of your frogs better than ever: they're cheaper to play and hungry for power.
So you have to build your own deck, but it's all-access. I like it. There are 13 possible commanders (that search says 14 but I'm pretty sure you'll only be able to use the rebalanced Uurg, not that you'd want to use the original anyway), and you'll definitely at least be in either green or black.
"Cheaper to play and hungry for power" might indicate the same emblem as last year: frogs cost 2 less and when a frog ETBs, you may sacrifice a creature to draw a card and have the frog gain all the abilities of the sacrificed creature.