Unlocked for purchasing all of Dante’s skills which will cost you around 320,000 proud souls.
Difficulty: Sons of Sparda
All the other guides posted are really great resources. I kind of got tired of grinding mission 3, so I would change it up with mission 12. I set the difficulty to Sons of Sparda. It's important that you not get hit to maximize the amount of proud souls you receive. Just kill all of the scarecrows in the first room then press systems, then retry mission. Depending on how good your style meter is, you can average about 600 - 1000 proud souls per try.