The Mewtwo Gold Star features a stunning alternate-color illustration that replaces the character's signature purple palette with a green and yellow color scheme, creating a visual that is immediately striking, unmistakably premium, and utterly distinct from every other Mewtwo printing
The real power is likely to be the cards activated ability, which costs X to activate and reads: Exile Karns Sylex: Destroy each nonland permanent with mana value X or less
This makes sense, since both sets were the first time back on planes which had pretty underpowered sets the first time around, so perhaps were righting the historical balance at WotC
Aminatou, Veil Piecer leads the deck Miracle Worker, which is all about the Miracle mechanic
Commander is a social multiplayer format, so all you really need is a playgroup, enough table space for everyone, and at least one person who remembered to bring dice
Varchild, Betrayer of Kjeldor could be fun in some sort of group slug deck where you give your opponent tokens but in a harmful manner (maybe with something like Trespasser's Curse on the battlefield), although she might be better in the 99, since mono-red is pretty limiting