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Rampant Frogantua's second ability counts every player who has lost, no matter how the player lost the game: due to a state-based action (having 0 or less life, trying to draw a card from an empty library, having 10 or more poison counters), because of a spell or effect that states they lose the game, because your awesome might has left them with no choice other than concession, or for any other reason
No matter how your opponent is trying to take you out, whether it's through combat damage, poison counters, Tendrils of Agony, or Archive Trap, Teferi's Protection pulls you out of the fire and keeps you safe through to your next turn
Teferis most common application is some kind of one sided Defense Grid which also gives sorceries flash and interacts with the battlefield while replacing itselfwhat
The four sets that will be rotating are Guilds of Ravnica, Ravnica Allegiance, War of the Spark, and Core Set 2020