Simply countering your first Polymorph effect is likely enough to take you out in a lot of games, since that leaves you fully exposed on board and way behind in tempo
Per the announcement, this allows for cards with game effects that would otherwise never be on the same card, such as the Reckless and Resist keywords
It's considered one of the best and most beloved Limited formats of all time, near-perfect in the hearts of many drafters due to its setting, mechanics, factions, and generally slow, grindy gameplay
But before you play "Amonkhet," it would be appropriate to remember some of the strangest cards that Magic has ever seen
Something playing Marionette Master or Mayhem Devil, perhaps
Sure, you won't see Poison Dart Frog appear in many eternal formats, and even that much utility might not be enough for Modern, but in slower Magic: The Gathering formats like limited or Commander, this little guy is an easy addition