Edit - Due to the amount of people who mistakenly completed the game on Diabolical and did not get the achievement. I'm putting this before the guide as to hopefully prevent people from doing this. - DO NOT COMPLETE THE GAME ON DIABOLICAL - I repeat, DO N.O.T complete it on Diabolical. Do it on Mastermind as the achievement itself suggests. This game does not count lower difficulties like most games do.
You must create a black skinned character from the beginning of the game. You CANNOT change this later and still get the achievement. There is a time early on in the game when you select your combat difficulty, this is the time to select Mastermind. Do not change it back until you have beaten the game and unlock the achievement.
Some tips.
- Don't be afraid to complete this game in one playthrough, you can change difficulty after end game.
- Stock up on Moses summons, always have at least 2 with you. And revives!
- After unlocking the ability to use moves from all classes, make use of the psychics ultimate healing ability, as well as the other minor healing ability. They are pretty much essential when dealing with the last few bosses. At that point, think of your main character as a healer, not a fighter.
I AM CULLY pointed out that you can use your summon's 10x each during a play through.