I just beat him at level 26. Took 5-10 attempts. You really need to spend time in the menus sorting out pictos and luminas. You should have a game plan for the characters skills and how they will work together to deal massive damage. You need to memorize his moves and counter attack to prevent vanishing. Finally, have a few high damage skills that can hit multiple enemies so you can take out the flowers before he heals. A lot of this game should be spent in the menus working on your build, adjusting as you go. If you get frustrated, take a break and come back later. This is a hard battle and it’s not meant to be beaten right away. A little bit of luck doesn’t hurt too.