If I play {Angel's Grace} during my upkeep, I have no cards in my library or I do not have mana to pay {Pact of Negation}, will I lose the game?
You will survive. {Pact of Negation} has a triggered ability that goes on the stack. Once that is over, it won't trigger again which means nothing will happen if you can't lose the game when it does trigger.
Quote from: Noblellama on January 02, 2014, 12:01:47 PM
I'm not sure... The pact says at the beginning of your upkeep you lose, would you have time to cast angels grace?
You have time. Once the pact's trigger goes on the stack, you cast {Angels Grace} in response. Since you can't lose the game, you're good to go!
Rule 101.2 When a rule or effect allows or directs something to happen, and another effect states that it can't happen, the "can't" effect takes precedence.
Example: If one effect reads "You may play an additional land this turn" and another reads "You can't play land cards this turn," the effect that precludes you from playing lands wins.