There are 5 main stats: Max HP, Attack, Defense, Magic and Skill. All 5 attributes of a hero can be increased through means of Promotion, Boosting, and Leveling.
There are also 3 secondary stats: Accuracy, Dodge, and Crit. These stats are calculated as a percentage.
A Hero's Equipment also affects their stats, although this can be an increase or decrease. A good example is the Black Iron Helm, which postively affects Defense and negatively affects Accuracy.
Max HP[]
HP is a two letter designation for Hit Points or Health Points. Characters lose HP when they take damage in battle.
The amount of Max HP is also the highest up to which a hero can be shielded.
Attack[]
A Hero's Attack stat determines the offensive power of any basic attack (i.e. even a Wizard's standard attack action). Most basic and skill-based attacks use this stat to determine their initial strength.
It is countered by the Defense stat.
Defense[]
The Defense of a hero determines how strong your Hero is against physical damage. Magic type attacks ignore the Defense stat.
Magic[]
The Magic stat of a Hero affects two different things: the defensive strength of your Hero against magic-based attacks and the strength of your Hero's shielding spells. Physical type attacks ignore the Magic stat.
Skill[]
The Skill stat of a Hero affects the in-battle Accuracy, Crit, and Dodge chance in combat.
Skill is comapared in-battle between two characters engaged in an attack. The character with higher Skill will have a better chance to dodge incoming attacks, and to land outgoing attacks - or criticals - on the enemy.
Accuracy[]
Accuracy (or Hit) is the percentage chance to land attacks during battle.
Height gives a bonus to damage and hit chance for every height unit above the target. The higher up you are, the more damage and the more guaranteed your chance to hit.
Critical[]
Critical Chance (a.k.a. Crit) is the percentage chance to deal extra damage(and sometimes additional effect) during an attack.
Dodge[]
The percentage of Dodge determines the Hero's chance to avoid attacks from enemies.