+1, +2, +3 respectively. And the chance of it triggering is as follows: 4.2%, 8.3%, 12.5%. This is also mentioned in the reference: Sheet 14, "Objects on the map that allow you to gain morale, luck, mana, and MP."
Then this confuses me even more...
In a race, during the final battle, the hero has +1 luck. When using a spell, luck becomes +3, even though the Air skill is absent... How can this be explained?