Magical Damage is an offensive attribute and affects a character’s ability to inflict damage with magical attacks and spells. Characters with a higher Magical Damage attribute will inflict more damage with magical attacks and spells.
Classes like Sorcerers, Spiritmasters, Gunners, Aethertechs and Bards, who rely on magical attacks and spells to inflict damage to their targets, tend to have the most Magical Damage, though Clerics and Chanters can also benefit from more Magical Damage.
A high Magical Damage attribute is important for classes that inflict magical damage. Physical damage classes, like Gladiators, Assassins, and Rangers, receive little to no benefit from Magical Damage.
Every 100 Magical Damage increases the damage of the skill by about 10% of the base value (the value with 0 Magical Damage and 100 Knowledge).
Ex.) The base damage of Weaken Spirit is 1,968. 100 Magical Damage will increase it by about 197 to a total of 2,165.
1 additional Knowledge increases the base damage by about 19.7 but does not change by how much your damage will increase with each additional Magical Damage.
With 0 Magical Damage, the damage you deal with a skill will be equal to the one provided in the in-game skill tooltip.
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The damage in the skill descriptions on this website match when your Knowledge = 100 and Magical Damage = 0.