Ultimately, any mechanic that alters the fundamental rules of the game across all formats should be considered incredibly carefully, especially when it will drastically warp all future gameplay around a handful of new cards
Now if your opponents play a sweeper, you can temporarily remove all your cards from play via phasing, only to have them return to the play again on your next untap step
Under the Skin Under the Skin is a sleeper hit
Offering two bodies and a mana sink for three mana is solid, but what puts Minsc over is that the X ability can be used as a sacrifice outlet but paying zero
Teferi's Moat "He's not red
(Equipment, Auras you control, and counters are modifications.) An Aura controlled by an opponent does not cause a creature you control to be modified