Theros Beyond Death will be the first Magic: The Gathering Standard set of the 2020 cycle announced back in September (see "Wizards of the Coast Reveals 'Magic: The Gathering' Sets for 2020")
I think itll be a one- or two-of in the sideboard given that decks choices in 3-drops
It can support your Active Spot mon by adding an additional 20 DMG off the mill and tearing down the opponent, or go to the Active Spot itself and deal 80 DMG
Whenever one of these cards enters the battlefield, players put The Ring emblem into play and assign a creature to be their Ring-bearer
Even in a depowered deck, you can find Salt Marsh, Jwar Isle Refuge, Frost Marsh, and Secluded Glen to make the other colors in a deck built around The Mimeoplasm or something
Even if this commander is countered, you still get to exile half of one of your opponents libraries