During combat (and only during combat), the Hero is considered to have a Resistance bonus of +30, essentially making the Hero completely incapable of failing any Resistance roll! Any effect that forces the Hero to make a roll will fail automatically. This includes enemy spells, Curses, and even Special Attacks.
The Charmed ability has only one level - there is no such thing as "Super Charmed". It is quite a powerful ability nonetheless.
There are many evil and destructive magics in the world that do not do physical harm per se - but rather attack the essence of a creature, its mind, or its very being. Such magics can be very dangerous, and can undermine or even kill a creature. Only the toughest, or those enjoying magical protection, can overcome such effects.
Charmed Heroes are exactly those who have found some way to ward off evil magic in some way or another. Whether it is a magical shroud that protects them, a divine being that watches over them, or even an artifact they carry around - there is no force in the world that could hope to overcome such protection. Though the Hero may still suffer physical harm (whether magical or otherwise), his/her essence is nigh invulnerable.
The Charmed ability is automatically triggered whenever the Hero enters combat, and will remain active until the end of the battle. While Charmed is active, the Hero receives an invisible bonus of +30 Resistance, rendering him/her effectively immune to a wide variety of ill effects.
The bonus is not seen in the Hero's details panel, but it is there. It's so powerful that whenever the Hero is forced to make a Resistance roll for any reason, he/she will never fail it - regardless of how powerful the malediction.
Virtually all Curses rely on forcing the target to make Resistance rolls, and do not work if the target succeeds its roll. Therefore, Curses will not affect a Charmed Hero. There are some Combat Instants and Combat Enchantments that also force their target to make such rolls, and again will not be able to affect the Charmed Hero either.
The majority of Special Attacks work in a similar manner - forcing the target to resist or die, or perhaps suffer a certain amount of damage. Once again, since the Charmed Hero does not ever fail such rolls, he/she will not suffer any harm from these attacks. Note that Thrown Attacks and Breath Attacks, while considered Special Attacks, do not work based on Resistance rolls, and thus can still harm a Charmed Hero as normal.
Remember that Charmed only takes effect during combat, and only for the duration of combat. On the overland map, the Hero is not immune to ill effects - he/she must make Resistance rolls as normal, using his/her unmodified Resistance score.
Improvement Table Edit
Charmed is one of the few Hero Abilities that does not improve with Experience. It is already extremely powerful even when the Hero is at Level 1 ("Hero"), so there would really be no point in improving it anyway.
Heroes with Default Charmed Edit
There are exactly 4 different Heroes that possess the Charmed ability by default each time you play the game:
Charmed as a Random Ability Edit
The Charmed ability is found in all Random Ability categories. Any Hero with at least one Random Ability pick that does not already possess Charmed may occasionally acquire it at random. There are no fewer than 23 different Heroes in the game that may do so: