Worlds will Collide this Saturday, as we bring together legendary creatures and planeswalkers from across time.
This Saturday you can pick a commander (including a planeswalker) from Dominaria United to be your commander, if you do you can have one other commander as long as it represents the same character.
For example you could run Liliana of the Veil from Dominaria United, and have Liliana of the Dark Realms from M14 as your second commander.
No, Braids Cabal Minion still isn't legal, sorry