Mindpower is the amount of principles you can learn. When you enter the game you are Mindpower 3 and can therefore learn 3 principles.
Heretic Archer Principle StealEdit
During a testing period Heretic Archers could "steal" principles from others, Due to a bug this also meant you could learn more than your Mindpower and also gain a large amount of principles. After this most people gained up to 11 principles. This was adjusted when you logged in due to the large amount of people affected. However as the system just picked the 5 (or correct amount) highest principles then some people lost the principles they choose.
Currently only 4 Mindpower levels can be accessed normally.
Mindpower 2 - This is left over from tests and when previously you would enter Magicduel at this stage
Mindpower 3 - This is the Mindpower stage you begin at
Mindpower 4 - Attained after advancing through the Story Mode from Mindpower 3
Mindpower 5 - Attained after advancing through the Story Mode from Mindpower 4. This is the stage where many will finish at.
Mindpower 6 - This stage is meant to be temporary, most people will visit it at least once.
Mindpower 7 - Currently a special level, can't be reached in normal ways.