From Golden Sun Universe

Luck is the statistic that determines a character's chance of being inflicted by a status inflicting problem attached to an ability used against you, such as Sleep and Stun.

It does not increase your own chance of inflicting said status effects onto opponents, contrary to common belief. Having a luck rating of 40 or higher provides immunity to Poison, Venom, Haunt, Death Curse, the target's HP being instantly reduced to 1, and being forced out of battle (Like the Djinni Gale's attack would otherwise have a chance of doing).

This means that any boss with a luck rating below 40 is in fact able to be affected by any of the above status conditions. All bosses in Golden Sun have luck ratings that would at least somewhat discourage trying to instant-kill them or afflict them with Venom, but with the exceptions of Saturos, the final encounters on top of Venus Lighthouse, and Deadbeard, it is otherwise quite possible to cause these effects to trigger on these bosses. Though in The Lost Age on the other hand, the only bosses that aren't immune to these status conditions are the Chestbeaters at the beginning, the Sea Fighter minions of the Briggs encounter, the Knight minions of the Moapa encounter, and the Ball minions of the Star Magician encounter.

Luck-related formulae

Any effect in the game that does not carry out with a flat success chance (like the innate 60%, 70%, and 90% chances of Quartz, Spark, and Dew, respectively) has its own base success chance that is lowered by the height of the target's Luck rating, and is also modified by the difference between the user's elemental level and that of the target, whether the target's element is its elemental vulnerability, and whether the target is a non-central target in a multi-target effect. The formula is as follows:

effect success chance = ((base effect chance + (25 if the target is vulnerable to the specific effect) + ((attacker's elemental level - defender's elemental level) - Floor(defender's luck / 2) * 3)) * (area multiplier))

Put more simply, for every 2 Luck you have, all base effect chances against you have a subtractive 3% taken away, and every Elemental Level you have over your attacker matching the element of the chosen move also takes away 1% from the base chance. Every elemental level the attacker has over you, however, adds 1% to the chance, and 25% will be added if your current Class has that effect as one of its very few hidden "effect susceptibilities." There is no additional benefit to having 3 Luck as opposed to 2 because luck-provided effect-chance-decreases only occur every other point, on even values.

The area multiplier in the above equation is .6 for when the affected enemy is one position away from the central target of a multi-target move like the Delude Psynergy, and .3 for when the affected enemy is two or more positions away.

The base chances for the effects in the game that are affected by the enemy's Luck rating are as follows:

Effect Base chance
Delusion 65%
Death Curse 60%
Haunt 25%
Instant Death 20%
Poison/Venom 55%
Seal 55%
Sleep 45%
Stun 40%
HP Draining 65%
PP Draining 60%
Ignore half Defense 50%
Lower HP to 1 35%
Debuff Attack 60%
Debuff Defense 70%
Debuff Resistances 75%

To summarize with an example, an Adept with 2 or 3 luck will only have a 17% base chance to be afflicted by an Instant Death effect aimed specifically at them (presuming no differences between their Elemental Level and that of the unit attacking them and presuming that the Adept's current class is not susceptible to Instant Death effects). Equipping a Jeweled Crown to raise their luck to 7 or 8 will reduce this base chance to 11% or 8%, respectively. These values, in turn, will respectively become 6.6% and 4.8% if the Adept is one space away from the member chosen as the central target of an effect spread across an area, and it will be 3.3% and 2.4% if the Adept is at least two spaces away.

Ways to increase Luck

Unlike your other statistics, Luck does not increase as you level up. Luck cannot be temporarily changed during battle, either. The only ways you can change an Adept's Luck are:

Gameplay elements and mechanics
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