This also makes it easier to convert, because you don't necessarily need to conquer a province with the Cathar faith, imprisoning a Cathar woman and making her your concubine would also work. that will make it highly likely for the Cather heresy to appear.

Then Catholic religious authority should be at around 30%.

So if you want to become a Cathar Emperor of Britannia, you could start out as Scandinavian Norse pagan, and conquer England (which inludes the Holy site of Kent), Cologne and Santiago in Hispania (unless the Muslims beat you to it). The chance of the Cather heresy appearing increases with every Catholic Holy site not controlled by Catholicism. My personal favority is moving my capital to a province with the Cathar religion and then use the decision to convert to local religion (requires the Sons of Abraham DLC). Check out : for how to become a Cathar then. This might take 100 oder 200 years, but unless Catholic rulers are particularly lucky with holy wars, it will happen rather soon. I don't think that the Cathar religion actually is in the game at the 769 or 867 start, so you first need to wait for it to appear.

they add some challenges, but give a lot of points. If you want to use the ruler designer, you might want to consider adding negative traits like lunatic or possesed.

Crusader kings 2 cathar