This is incredibly powerful, but the symmetrical effect makes it a real build-around card
For whatever reason, I never got into Magic: The Gathering or the Pokmon trading card game as a kid
Your opponent is going to have countermeasures, and by diversifying your sideboard package you force them to diversify those countermeasures, which means bringing in more cards than they would like and cutting into their core pieces
With that in mind, I think were most likely to see Merfolk and Pirates team up to lead naval battles against the Phyrexian invasions
While some people have argued that Wizards would find a way to adapt and move forward like the music industry did in response to its piracy problem, perhaps by taking the game completely digital, personally, I don't have much faith that Wizards could completely reinvent the booster pack model it has been using for 25 years and be successful
Streets of New Capenna Streets of New Capenna had a hybrid rare creature cycle, but it tried something a little different