Another mash up for your enjoyment: Magic the Gathering vs Final Fantasy VII
((How does a life total become 1 “UNTIL THE END OF TURN”!?))
((I assume that it means that unless they lose the game before the turn is over it goes back to where it was previously? It would be a new mechanic because MTG doesn’t account for stuff like that))
They would lose difference between their current total to make 1 life. They would gain it back after. A new rule would have to be put into place to make this not trigger things that look for life gain/loss (Ajani’s Pridemate, for example). It’s also more for flavor since Sephiroth has, in game, an attack that reduces the target’s hit points to 1 (regardless of previous health).
No, they would lose the game immediately when the enters the battlefield trigger resolves. It’s a phrasing that’s been seen on cards like Phage the Untouchable, so it’s not a new thing.