After blocking creatures have been declared, even if no creatures are blocking, both players will receive priority before the combat damage step. An unblocked attacking creature can have its power raised at this point in order for it to deal an increased amount of combat damage. It is at this point that an attacking or blocking creature can be removed from play in order to prevent it from dealing any damage. Usually this is the best opportunity to use spells and abilities that increase or decrease the power and toughness of creatures in combat as it is the last chance to do so before the combat damage step.