How do I beat commantis (the grid) this is so hard(I know I'm bad at this game) wich level do you think I should be?

Dream Drop Distance and Birth by Sleep bosses are badly designed for the most part so I wouldn't necessarily say you're bad. What you want to do is try to block and counter aura the discs it shoots out at you (dodging will probably get you hit) and get in as much damage as you can when it's not attacking. Try not to move or dodge onto the edge of the arena and start a flowmotion grind because you might get caught in one of its attacks. I don't remember if you can remove the flowmotion command for grinding, but if you can, I'd take it off for that fight. 

As for the level you should be, the combat level of the world (can see on the world select menu) is roughly the level of the enemies there. If you want an easier time, try getting a few levels over it if you aren't confident enough in your play