Here's hoping the diancite gets released before this competition starts, seems like it would be an interesting mon to use in this meta.
also, here's hoping that marshadow gets released worldwide, bc wouldn't that suck :/
ngl i've been wanting a bss format with mythicals included for a long long time so i'm really keen for this format. magearna in particular seems like something i'd be really keen to look at as a blanket check to a lot of the things that are allowed in this format, such as genesect, hoopa, diancie, darkrai sorta, necrozma celebi etcetc. if anyone overreacts to the presence of marshadow and brings a scarf lele then magearna will punish that too. zygarde-complete and the deoxys formes will be broken, as will marshadow, so i'd imagine that most teams would need a bulky answer to cope with that pokemon. a particularly cool pick that i can think of would be tapu koko, for its ability to hard check keldeo, manaphy, hoopa i guess, skymin, darkrai (by blocking sleep and outspeeding) and marshadow (again, by being a faster fairy-type). seriously, 130 is such a fantastic speed tier for this competition and tapu koko has all the needed tools to make it work, at least in theory.
getting back to zygarde for a second, i feel like thousand arrows will have to be considered on every team that wants to do well. bug stab could be useful in this format for catching the numerous psychics (not to mention darkrai) offguard so i'd say that something like mega heracross or yanmega could potentially be useful here. old mate skymin will be by far and away the most common 1karrows switch-in tho.
e: btw baton pass is dead pretty much purely because of spectral thief lmao