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. You must declare that you are going to use the re-roll prior to the actual roll itself. If this re-roll is not used during that session, it does not carry over to the next. Foresight cannot be used to re-roll natural 1's; in this case, the use is not wasted. A single roll can only gain the benefits of a Foresight spell once.