I leveled up everything (regular levels, all forms except Final, and summons) going round that river place...what's it called... Timeless River that's it. Yeah, so you go to the dock and get your drive gauge as high as you can, then go to the next area, and get your gauge full, and then destroy everything else in there. Drive gauge empty, next area, destroy the cars (this CAN be difficult) and get your drive gauge a little higher, go to the area with the save point, save, sell stuff, buy stuff, wrinse and repeat.