Arena has featured a few different types of cubes: Their typical Arena Cube, the Arena Powered Cube, the Chromatic Cube, and the Tinkerer's Cube. These are all phantom events restricted to cards on the client and change significantly with each iteration
Green decks wont have any issues
Its a singleton deck, meaning you cant have more than one copy of any card thats not a basic land (so in a Black deck, you could have 20 Swamps, but you could only have one Witchs Cottage)
Cavern of Souls, Roaming Throne, Adaptive Automaton, and Banner of Kinship are some prevalent examples
Before we move on, I just want to mention that for some reason (like design) this isnt an energy commander
And not only is the Tergrid player getting these cards but the other players are losing them