Plus in some tic tok videos there are more spoilers. We now have most of the key mechanics for the set spoiled.
Initiative is like Monarch and Venture into the Dungeon had a baby. You can take the Initiative (which is a Monach like card), when starts or continues you Venturing into Undercity (unlike you've already started Venturing into a Dungeon in which case you continue moving thru that Dungeon until competed) and once you already have the Initiative you keep Venturing during your upkeep or when something let's you take the Initiative (you can take it still when you already have it.
Backgrounds are Legendary Enchantments that buff your Commander (and sometimes they do other stuff as well), that can be your Commander if you also choose a Legendary Creature with Choose a Background.
One card had Myrid mechanic on it, but I don't know if that is a Precon card or in the main part of the set.
The return of Dice confirmed.
Return of Modal cards & treasures like AFR.
Adventures are confirmed to be returning. This should please Eldraine fans.
Bhaal is in the set and in Riveteer colours (Black, Red, Green) and has indestructible if you only have half your starting life left or less. When your creatures die, put a + 1/1 counter on a creature and Goad it. I'm curious if this unique approach to Indestructable will be a common trait of Gods in this set.
Most of the reveled Legends have somekind of tie to BG, (BG1, 2, 3 characters as well as Descent: Into Avernus). Imoen, Mizzy, Jen Janson, Jheria (indirectly mentioned), and Savatork (BG1 Bad guy) are back along side BG3 characters like Lae'zel, Gale, Wyll (indirectly mentioned), Raphael from BG3. No new Planeswalkers spoiled.
Red gets a redirect spell with dice rolling that is spicy, named after Wyll.
A red dragon that basically turns all your Dragons into taunting basher.
Just so much to digest.
Oh text plothook basic lands are back and the set has its own version of Gate Lands. One Legendary Creature collects gates, which suggests the set has at least 9 of them.
Wizards of Thay is a card, it's the one with Myriad.
Raphael (R/B) batches Demons, Devils, Tieflings, and Imps, gives them +1 and Lifelink.
So far looking mechanically very fun set, sooooo excited for it and it's a Arena sister set, Alchemy Horizons: Baldur's Gate.