If you play Pact of Negation and win the game before your next upkeep, but would have been unable to pay the 3{U}{U} mana cost at the beginning of your next upkeep, do you still win?
"A game ends immediately when a player wins", among other circumstances (C.R. 104.1). (Any triggered abilities scheduled to trigger at a later time, simply don't trigger after the game ends this way; this applies to the one from Pact of Negation just as it does to, say, "Draw a card at the beginning of the next turn's upkeep".) See also this thread.
If you play Pact of Negation and win the game before your next upkeep, but would have been unable to pay the 3{U}{U} mana cost at the beginning of your next upkeep, do you still win?
You can't be sure you'll lose next turn. Someone might play Eon Hub!
Anyway, no game in the world would deny a victory because 'you might lose next turn'!
Anyway, no game in the world would deny a victory because 'you might lose next turn'!
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules