The way these cards are working is identical to how Ikoria: Lair of Behemoths did its tie-in with the Godzilla universe, where cards from the set have alternate art but are still treated as the same game piece
Remember, we're only 80-ish days away from the unnamed fall set and rotation, Commander 2019 is being released in a little over a month, and then fall set spoilers should start around the beginning of September
It does require that your opponent have some cards in their graveyard, but this will more than often already be the case
I'm not sure if this will reignite the Delver hoards, or even take much play percentage from the Wizard's Lightning decks, but I do know that Delver players will be out in force in the coming weeks to find out
The other modes are good in any kind of Golgari midrange, so you get a Putrefy and a super Regrowth
On the land side, five pixel lands apply a retro video game look to the basic Plains, Island, Swamp, Mountain and Forest cards, with an added frame that evokes old-school Microsoft Windows with a title bar and minimise, maximise and close buttons