During a rest, your character may spend a portion of that time planning ahead for the upcoming battles, puzzles, trials, etc. During a long rest you may roll 3 d20s and add your proficiency bonus to each of them, during a short rest you may roll one d20 and add your proficiency bonus to the roll. Keep track of the totals individually, these are called your preparation dice. After the rest you may choose to use one of your preparation dice instead of rolling for an attack, ability check or saving throw. When a preparation die is used in this way it cannot be used again, all preparation dice expire during your next rest and you may roll new preparation dice accordingly.
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