Jace, Wielder of Mysteries
Oracle Text
If you would draw a card while your library has no cards in it, you win the game instead.
+1: Target player puts the top two cards of their library into their graveyard. Draw a card.
-8: Draw seven cards. Then if your library has no cards in it, you win the game.
From what I can tell, the -8 only wins you the game if:
A) you have exactly 7 cards in your library, or
B) You have fewer cards but Jace survives ulting (9+ loyalty before activating)
Is that accurate?
116.3a The active player receives priority at the beginning of most steps and phases, after any turn-based actions (such as drawing a card during the draw step; see rule 703) have been dealt with and abilities that trigger at the beginning of that phase or step have been put on the stack. No player receives priority during the untap step. Players usually don't get priority during the cleanup step (see rule 514.3).
116.3b The active player receives priority after a spell or ability (other than a mana ability) resolves.
116.3c If a player has priority when they cast a spell, activate an ability, or take a special action, that player receives priority afterward.
116.3d If a player has priority and chooses not to take any actions, that player passes. If any mana is in that player's mana pool, they announce what mana is there. Then the next player in turn order receives priority.
120.4. A player who attempts to draw a card from a library with no cards in it loses the game the next time a player would receive priority. (This is a state-based action. See rule 704.)
Technically, while you are drawing cards, if you have less than 7 cards in your library, you have to wait until the ability resolves BEFORE you regain priority. Order of operations is:
1) 6 or less cards in library. Pop ultimate.
2) When ability triggers, draw 7 cards. Priority is lost.
3) Ability resolves. You win the game since you had no cards left in the library.
4) You regain priority. Doesn't matter. You still won.
You're right in that it seems like that's what they're intending this Jace to do.
Assuming that's the case, I wish they had phrased this card differently. Even if it's technically right because of that rule, it will cause large amounts of confusion between the handful of people that know of the rule and the majority that have no idea. I'm mostly thinking about Limited events where the level of rules knowledge is lower.
I also really hate that some state-based effects wait for priority and some don't. It's an unneeded complication.
I mean, that seems to be in the general flavor of what this card "should" be doing... but I'm not sure that wizards would bring up such an obscure timing rule for this purpose.
-8 to pay for ultimate.
Jace has 0 loyalty.
Jace goes to the graveyard.
Now his ultimate effect occurs.
Draw 7 cards.
- was there more than 7? OK. Keep playing.
- was there less than 7? You decked yourself.
- was there exactly 7? Then if your library has no cards in it, you win the game.
If Jace had more than 8 loyalty and therefore is still on the battlefield, If you would draw a card while your library has no cards in it, you win the game instead is relevant. Otherwise, it's not.
So, yes ... your statement is accurate.
This Jace plays nicely with Jace, The Mind Sculptor, since you can Brainstorm and then Thought Scour yourself. They do both cost four though, a pretty contested mana spot.
T2 island, puresight merrow, paradise mantle, equip mantle to merrow.
T3
untap
upkeep - activate puresight merrow any number of times until this Jace is on top.
Draw step - draw the jace
Main phase - play the jace, activate puresight merrow and exile your library. Uptick jace and win.
What happens is...
Jace is at 8, you have, say, 5 cards left.
You ultimate Jace, his ability goes on the stack. He dies as a state-based effect when you next receive priority.
Priorities are passed and the ability begins resolving. You complete all of the instructions on the ability before receiving priority again: you draw seven cards (but can't, so you only draw five. You try to draw a sixth, but can't, so next time you would receive priority, you lose instead.). But for now you keep going. Next sentence: "If your library has no cards in it (it doesn't), you win the game". So, complete those instructions. You win the game.
Boom, game over, you win. Go get yourself a victory soda.
You never actually lose because you won first, before you would have received priority again. Note that this also does not count as losing and winning at the same time; in this specific case you win immediately before you would otherwise lose.
Yrrej8611 above goes into more detail about the actual MTG comprehensive rules that determine all of this.
tl;dr: his ult is confusing because it wins you the game immediately, whereas 'decking' yourself out doesn't actually cause you to lose until after you've done everything the ability says (not just the first sentence).
I was not 100% sure on the ruling myself, so I searched the rules. Rules 116.3b, 116.3c, & 120.4 are the rules if anyone is interested in why you'd win.