So there is going to be a new format for Arena called Alchemy (love the name), which is basically standard, plus new cards from digital only sets tied to premier sets.
So the first Alchemy set is primarily tied to Crimson Vow, BUT it's a special Alchemy set because it will have new digital only cards for all the standard legal sets.
This means this 63 card digital only Alchemy Set will have Digital Only cards for Zendikar, Kaldheim, Strixhaven, Forgotten Realms, and Innistrad (which it will lean into).
Everyone on Arena will get 3 free Alchemy packs and some free Alechemy cards to start things off.
These cards will be legal in what they call Live formats and Alchemy, but not on what they call the paper formats (or Arena's equilivant to paper formats).
So they are legal in Historic Brawl, Historic, and Alchemy, but not legal in Standard or Brawl.
I suspect they will have a digital only Elminister Planeswalker or Creature, that will have Spell Book,like a couple of cards have, that the card will conjure cards into you hand or library from.
It might have Jarlaxle too or other commonly requested D&D characters too.
Oh one weird think is the new Spider Legendary Creature from Innistrad has her own Spellbook, they you can draw cards from,and one of those cards in her spell book, is a DRIDER, so does this suggest Driders are a thing in Innistrad or at least in MtG in general?