In this video I begin at the final save spot on the third floor of the Neameto Float. Before this final battle I defeated the four masks in order and Atman in the grave yard to secure the good ending of the game. For those of you who don't know. Late in the game you will get a oath grail from Joshua in the London rats head quarters after the whole orphanage and mental hospital stages in London. I believe he asks to borrow your slingshot first which I responded to as "Yes".
From there you can learn the pattern to defeat the masks by looking at the grail description in your valuables menu. The masks must be defeated before speaking to roger bacon to go to Neameto, before Alice gets sucked into the grave yard a second time. In a nutshell it says to fight them in this order: Grail, Gold, Staff, and Sword. So what I did was go increase my malice to red and then go to the blue castle tower. I did this so I did not have to spend a lot of time fighting enemies in between the mask random encounters. The enemies here are weak and can be mowed through easily. Besides, with each mask netting you 45,000 experience points, I was not looking for any grinding at this point in the game.
From here I fought each mask in the corresponding order once and only once, running away from duplicate battles with previously defeated masks and other masks which arrive out of the order. If you go in the order of the oath grail the mask defeated before will cancel out all the nasty effects of the following masks with the only effects gained at the first battle with the grail mask which are positive ones (double hit area).
Eventually you will fight and defeat all masks. At this point save your game and head to grave yard. Get rid of your malice and examine the grave stones. When you are ready go to roger bacons' Nemeton Monastery and enter Alice's dream sequence. Have her look over all the grave stones a couple of times and then go to the atman fight. If you did it right Yuri will show up and help you defeat the boss to secure the good ending.
From here I fight Cardinal Albert Simon's final form. During this fight I used Forron and basically buffed up my attack power so I could take care of him in a single attack with the help of the seventh key.
Once Albert takes a thrashing, I arrive at the Meta-God on the stratosphere. Of course I abuse the buff stats with the exception of the physical strength move I used in the fight before. This was skipped because he will negate all status effects each time you try to buff in this manner. After this I just ran wild with the key items and the monkey paw for the final combos to finish him off.
I could have fought both of these fights the old fashioned way but I figured I have had these items sitting around in my inventory up to this point, so I might as well get some mileage from them.
After the battles you get the good ending and the credits of the game.