Rising Waters was the core of the last top level Prison deck, using overpriced versions of several components to gain favorable or even match-ups against everything else in the format
So long as you're playing with a bunch of cards with good enter-the-battlefield triggers, like Skyclave Apparition, Agent of Treachery, and Deadeye Navigator, you can rinse and repeat until you've taken over the game
The cards needed to finish them are incredibly rare pulls from packs, which you can get a sneak peek of by tilting each pack as you open it
MacCready has never been reprinted since Universes Beyond: Fallout released in March of last year (and likely wont be, given the legal hoops of licensing IP), so its had the most to gain from this surge in demand
And we're taking them off the list today
The stats are more than solid, and punishing your opponent for killing your early creatures is awesome