Oh come on now... (Fairly large spoilers!)

[DragonXVI]

...5 Forms? What is this... Final Fantasy? "Hurray! He's Dead!" "Oh wait no, now he's HUGE!"

(Admittedly that was quite awesome)

For the record I still haven't beat him.  Last night's attempt got me to the last form before I ran out of food (I wasn't exactly a well stocked kitchen to begin with though), but should be slain this evening now that I know what I'm actually doing.  At least now the intro's starting to make a bit of sense

Also, Dual Form = Yes.

But still, did you guys just not decide on what the Final Boss should do and just went for everything? :p

[Don Andy]

When I saw he had that many forms I was pretty much "WTF", too, but in the end I only found the 2nd form to be a challenge. The first form was pretty easy, once you got the pattern, the third form is a joke, the fourth form is an easy form of Simon, and the last boss really only looks tough. The hardest part about the last form was figuring out what to do with the ball thingy on his head.
And if you're good with dodging and pack lots of poison cures, the 2nd form really isn't that hard either.

Jelly costume and Spirit Form are a must though :p

[Xiagan]

Jelly costume and Spirit Form are a must though :p

I second that. With it, you don't need much food for the last form.

[Lambchops]

Actually I can do most of the last form without getting hurt too badly and without spirit and jellyfish (not the first time but certainly now). It's actually really easy to dodge his projectiles. Go fairly close to the orb when he fires them then just before he does boost away and then start swimming in a fairly tight circular motion and the homing particles should circle harmlessly around you until they dissipate. I used a similar tactic to avoid the thornworms in the kelp forest boss. It works pretty well for some (but not all) homing projectiles (and fails utterly if there are several enemies firing them at you or if you don't have room to manoeuvre). Of course it gets a tad trickier when he starts spawning enemies, or when you're trying to figure out how to hurt him while dodging. However once you know what you're ultimately aiming for it's a fairly fool proof tactic.

[DragonXVI]

Wasn't having too much trouble with any of the forms except the 2nd took a bit of a beating.  The 5th seems easy, his projectiles are easy to avoid.  The guys he spawns are pretty annoying, but needless to say I managed to forget about Dual Form Think I died just but accidentally standing in front of one of the barrage's and taking 5 flaming balls to the face

( ow )

[Lambchops]

My problem with the 2nd form was that I'd put all my ingredients into arcane poultices and so on and didn't have anything left to make a leeching poultice when I inevitably ended up getting poisoned. Fortunately the arcane poultices and energy shot boosts saw me through.