It's a rather hard boss, true.
First, eat the jellys in beast form for some extra health; don't even try energy form for these. If they oerwhelm you, you're dead. But try to have as many as you can handle on the screen, because then you'll be able to hit more with less bites. When it does its electricity spin thing, either dodge if you can, or have some +defense food. You can also try biting the center eye with some +bite soup for more damage, but this requires precision.
Pets help too. Try the blaster peg (or the piranha, but it's rather slow), and also have Li around for some extra firepower. Don't try to charge your shots if you use energy form to shoot it when you have some breathing room, just shoot away.
Oh and the reward is totally worth it.
