Foresight:

If successful, you may request a moderator re-roll any d20 roll, once, during the session in which you cast this spell, and take the desired result. If this re-roll is not used during that session, it does not carry over to the next. Foresight cannot be used to reroll natural 1's. You cannot cast Foresight to reroll a check that was already rolled. A single roll can only gain the benefits of a foresight spell once.