Okay, I might not be as perfectly detailed as you want be ill give it a shot:

This boss is easier than you think. When ever it is just moving forward, attack to head
on. At some point it will open up and start charging a missile looking thing, attack this
as much as you can. This missile thing is very weak when charging, but you must get out of
the way because after it is done charging it will quickly move forward to hit you. Another
attack this boss will throw at you is some power-ball like things. You can hit the block
butten when these come near you and they will bounce back to hit the heartless archers on
top of it.

Hope this helps!

ive done all that already...but sometimes it makes my screen move, and i cant move it back
so i cant block the fire-ball thingies...or dodge the barrels it rolls around at me...im
gunna save up all the money i get for xmas and hopefully buy a new ds by my bday :) then
ill have working L and R buttons xD

oh, and i wouldnt recomend using an action replay device with this game...cuz i tried, and
it corrupted my file...i gotta start all over again now

that last post thingy was me

The thing you are fighting is called an infernal engine, and I have passed this with MUCH
joy to go on. Sounds like someone hasn't checked the Heartless files. I suggest that. You
can find it under files in the ultimate pause menu in the grey area(lobby where you get ur
missions) Return the cannon balls (balls of fire) with a block(very useful pannel.) Then
when the hammer comes out (be sure you have stocked up on potions!!) Sacrifice yourself so
you don't have it push you up against the wall. When the balls come rolling out, KEEP
BLOCKING!! THe push you back and maybie to the side in the path of the other ones, so keep
blocking. The big battering ram that glows purple and rocks back and forth is its
weakness. JUST GET OUT OF THE WAY B4 IT CHARGES!! It does hurt you Dodge roll to get out
of the way fast. It comes fast. you should be able to beat it with these simple tecniques.
Please, I tried my best to explain, and I hope it helps.

i figured it out a long time ago and finished the game...the ending was dissapointing....

i didint liek when xion died but atleast u got sum aweosme poewrs

i didnt know xion died thx for telling my that :(

Thanks for the effin spoiler alert #$@#%@#

the game cameout two years ago and if u have it at the end dats wat happened.........

u need a lot of magic out just start hammering it out

you need a lot of potions to