To get to the best place to level in the game, you have to get past Mount Ordeal 3. I did a little searching around and found this page on the NIS America forum. It really helped me develop my strategy. My main damage dealer was a Mage using Omega Star instead of Desco. Unless your level is in the 2000-3000s, I think you will have to clear the board this way. Below is a video of how to clear it. I used a slightly different more time consuming approach.
I said it earlier, Mount Ordeal 4 is the best place to level. Once you get here, you will probably do all of you leveling here. If you want to get ridiculous amounts of experience, get to Mount Ordeal 4.
I saw my copy of the gem sitting bookshelf. I decided to take a look at Amazon to see if it’s in stock. It’s available for $22.40. That’s definitely a steal. Pick it up if you are a fan. If you have a copy maybe a there’s a someone in your life that could benefit from such an awesome game.