A lot more than most people would think, and more variants are still being discovered or released
TLDR: two is their answer.) I was medium on Hylda until I realized that the second mode puts a counter on each creature we control
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Yawgmoth combo, for example, competes in Legacy and Modern by utilizing Persist creatures combined with Yawgmoth, Thran Physicians sacrifice effect to draw your entire deck
Monsters with the Counters cannot be used as Material for anything else and get sent to the GY during the End Phase