If MJ, Rising Star is dealt lethal damage at the same time that you gain life, she won't receive a counter from her ability in time to save her
Speaking from the uninformed perspective of someone who's never opened an Unfinity pack, the set looks like it would be fun the first time you tried it, and then never again (outside of an Attraction Commander deck, which admittedly sounds like a laugh)
Premium foil cards are randomly inserted
As you can see mythics were on track to contribute just under $90 in EV (Estimated Value) to MM15 at launch
Of course, a card that packs this much Lore comes with a cost while Mirabel costs only 5 ink to play, she cant be played unless the player has five or more characters in play
The others went through a few rounds of brainstorming though