If you don't like Universes Beyond, this is your warning that you may want to avoid seeing new cards this coming week. For everyone else, preview people are listed here. While September 12 is the official start of seeing new cards, we won't be getting decklists until the next day. How it'll work is a bunch of folks will show off new cards, then by 2pm PT (aka 9pm GMT) we get someone else dropping the full decklist and the remaining cards. September 13 is for the Tyranid Swarm; September 14 for The Ruinous Powers September 15 for Necron Dynasties; and September 16 for Forces of the Imperium.
Now this was claimed to be from a dumpster dive
https://imgur.com/Hl2qlHw
If the picture matches in muddstah preview
Then the crediblity of mystical archive blueprint Mishra's Bauble gains credibility