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Spells typically have a flat damage roll depending on level. Spells that use spell slots usually can also be cast using a higher level spell slot than the spell itself, increasing its damage. Some spells may instead increase in damage based on character level. A few spells will also add your spell casting ability modifier to the damage.

If the spell's level spell slot is available, it will use it. Otherwise, it will use a higher level spell slot if available.
#tip