can someone please help me on this boss fight at the end of chapter 9 i get his health half way down but then he just launches attacks from everywhere, :)

Are you killing his shoulders first, or leaving them alone and targetting him directly? 
 
I find blowing away the four faces on his shoulders (right/left pauldron and right/left ...something else) notably decreases the amount of firepower you have to deal with.  After that, just wail on him til he starts charging a mega attack (His shoulders will open up and start charging), eventually he'll wince and then go back to charging.  After he does that wince, immediately switch someone to a Sentinel for a provoke/guard to soak up most of the blast.  Everything else is pretty minor and can be covered by occasional medicing. 
 
For my Sentinel Paradigm, I prefer Solidarity (Commando/Sentinel/Medic).  The COM will keep the chain from dying while the sent and med do their thing.  Go all out to stagger him between mega blasts if you want a good rating, because whenever he starts charging his chain gauge totally resets so you have to stagger him before that.

I used Light, Vanille, and Fang, I took down two shoulders and then I used Odin to blow away the other two pretty quickly.  After that I found most of his attacks not too bad.

Okay heres what you do. 
 

• Throw up a librascope. this will identify the elemental weaknesses of the shoulders.
• cast shell on your characters.
• attack the shoulders with their elemental weakness.
• when they're gone, the boss will have a lower stagger threashold and take more damage.
• switch to synergist and sabertour, he is vulnerable to slow, makes things easier, you will also benefit from shell.
• when he charges for his insane attack, relentless assault, if you don't damage him enough he WILL one-hit kill you.
• Damage him enough and the damage will go down to about half.
• sentinel, medic, medic for quick recharge.
• continue stagger.

 OMG OMG OMG 
 
Just did it on my SECOND attempt. Got 0 stars and it took me 21:22 mins but I don't care, that shit was crazy. 
 
I used Lighningt, Snow and Fang. Relentless assault when everyone was near full health (which was very rarely,) 2 sentinals and a medic when health was critically low and/or someone was down. Rest of the time Lightning was healing while Snow and Fang staggered as Ravager/Commando. Woudln't have done been able to do it without raise and Odin.
 
=)

Librascope and at least two Ravagers will take care of the shoulders very quickly.  Also, don't forget that Summon will bring your entire party back in with full health, so wait to pop it after you've gone all out.  Also don't forget that the stagger meter is reset after the summon leaves, so don't use it just to build up the stagger meter.  A Synergist doesn't hurt especially if they have haste.
 
It's a tough fight, stick it out and make sure you scour the room before for items.  There should be two rune bracelets there that prevent 10% of magic damage and if you upgrade well, you can easily get them to 20%.  That helped me alot.

I used Lightning, Fang, and Hope (and a few of those pre-battle buff items). I took him down after a few tries because he tends to cast Doom on  your main character and then you're fucked =}

I signed up just to respond to this post, this guy drove me crazy, I died repeatedly on him.  I could kill his shoulders no problem but he would always waste me with "Destrudo" even from full health.  I didn't realize for the first few attempts that you could attack him during the charge up and disable a few of the missles. 
 
This is the strategy I used: 
 

• Start the fight with a Fortisol (use it just before triggering cutscene) and Light (Rav), Hope (Rav), Sazh (Com)
• Blast the Right Pauldron (left most head from player perspective) until killed
• Switch to Hero's Charge; [Light (Med), Hope (Syn), Sazh (Com)] and let Hope Shell everyone
• Switch back to Relentless Assault and blitz the other three heads from left to right as fast as possible switching to Diversity; [Light (Rav), Hope (Med), Sazh (Com)] only to heal and then back to Relentless.
• Once heads are killed start hitting the main head to build chain again switching to heal when needed and switch to Hero's Charge (Sazh as Syn) for Haste when needed  
• When he starts casting Destrudo switch to Relentless Assault no matter what and start blasting him (using only Sparkstrike with Light; found that it did the best dmg for me).  After 2 full ATB bar charges and a 3/4 charge he usually groans and 6 of the lights go out (*2x in a row I was unable to stop Destrudo in time and he wiped me out anyways)
• After he groans switch to Diversity to heal up and keep increasing the chain bar, recast buffs as needed.
• Repeat till dead.

get rid of his goons on the shoulders, then start targeting the big man.  a sentinel would really help in desperate situations.  when he's charging up, heal up, then attack him with everything you have.  the more damage you do when he's charging, the less damage he'll do to you.  lather, rinse, repeat.

Well I gotta thank you guys in this thread, i kept dieing on Bert for about an hour and was finally able to whoop his ass using the advice in here. 
Thanks again GB community!

This might be slightly off-topic, but did anyone else get Doom cast on them in the battle the OP was talking about? The first time I fought him, I had him down to about half health and his ultimate attack put Doom on Lightning, and I couldn't beat him before the timer hit 0. I beat him on the second try without having Doom put on me, but I was just curious if anyone else had that happen to them.
 
Edit: oops, should've read all the posts. Guess I'm not the only one, then.

Worst boss fight in my entire life, died 40X in a row. I can finally take down his shoulders, I attacked the head before he used that beam that almost kills you, on the second time, I find that impossible to defeat him, I can't heal up in time. My party is lighting/vanille/fang, any other combination I get totally destroyed easily.  
 
I just finished it, I changed my party and still had enough hp now to start healing. One of the biggest advice I can give ppl is to use your libra three times for the shoulders and don't use it for one of the shoulders. Then you can still use odin against fighting that stupid head thing incase you need to heal. Odin will work against destructoid of whatever it's called, he can asorb the hit. Still I stayed alive using potions and had a good healer in my party. That was honestly a tough boss, without trying to figure it out online, there is almost no chance except to die over and over because the odds are totally against you.

If you are just getting the shit beat out of you then you might want to power level a little bit.  The room before the boss has plenty of enemies that re-spawn so that you can increase your party's HP or gather credits/premium credits to sell at the store.  Then using that money buy x36 Vibrant Ooze and some Turbojets to level up your weapons.

I had a lot of trouble with this boss, but there is one simple thing that you need to know to make it easy. When he is charging his doomsday attack or whatever it is called, attack him with your whole party until he makes a grunt sound. The attack will now only do half as much damage, and you can heal up pretty quickly.

This Boss took me 4 deaths before I said to hell with it, and cheated by looking up the strategy. The thing that makes this boss so difficult, at least for me,  is spending so much time healing and re-buffing, there really wasn't a big window to attack him with a RAV+RAV+COM Paradigm. I found myself slowly chipping away at his health, and even when I did get him to stagger he begins charging which basically signaled me to stop attacking and prepare (Buffs/healing) for the incoming Death blow. My fourth death, I got him down to a sliver of health, and then my Doom counter expired.
 
This Boss was frustrating to say the least, as everything up to this boss is an absolute cakewalk. I really wasn't prepared for such a difficulty jump. Turns out this Boss isn't so bad. It's just a simple pattern, using the proper Paradigms. It kind of irks me that  I had to cheat to beat him.

ya by the way i beat him, and i am stupid for not beating him in the first try, did one little thing wrong.

I think a lot of people here are making the mistake of going all-defense as soon as he starts charging.  Don't do that, he takes a long time to charge up.  You'll want to beat on him for a while, eventually he will flinch and grunt (like @lucas_kelly said).  After this point, you can switch to a paradigm like Protection (Sen/Med/Syn) or even Sen/Med/Com and prepare for the hit.  It will do less damage, and you'll have had a while to beat on him prior to the blast. 
 
Don't just turtle as soon as he starts charging or you'll never kill him.

" I think a lot of people here are making the mistake of going all-defense as soon as he starts charging.  Don't do that, he takes a long time to charge up.  You'll want to beat on him for a while, eventually he will flinch and grunt (like @lucas_kelly said).  After this point, you can switch to a paradigm like Protection (Sen/Med/Syn) or even Sen/Med/Com and prepare for the hit.  It will do less damage, and you'll have had a while to beat on him prior to the blast.  Don't just turtle as soon as he starts charging or you'll never kill him. "

Strange, I just beat this boss and had virtually no trouble with him
 
Despite the fight taking for what seemed like forever (because he resets his damn stagger-gauge), I found it to be quite easy, and was never in danger of dying.
 
I used Light/Fang/Vanille.

Having a nightmare doing this boss fight.
 
I can take out the 4 heads no problem.
 
Then i attack him til stagger and call in odin. This usually puts the boss down to 75% health.
 
Now he starts using his Destructo ability and this is where im having problems.
 
If i take a sentinel then i can just about survive this attack but by the time i get the boss down to 30-40% health he casts doom and i dont have enough time to kill him.
 
If i try and attack him while he's charging Destructo then i cant do enough damage to cause the mini stagger (that reduces the damage of his attack), i've tried RAV/RAV/RAV and COM/RAV/RAV multiple times and never been able to do enough damage.
  

What am i doing wrong?

Just got to this fight, must have taken me 20 minutes before the Doom took me down. I had him at about 8% on my first try. 5 more minutes and I would have had him. Well I recently came into a large sum of money so I decided to upgrade the hell out of Vanille's Healing Staff and some rings, maybe that'll give me the edge over him. I'll have to try ago tomorrow, calling it quits for tonight. >.>

" Okay heres what you do. 
 

• Throw up a librascope. this will identify the elemental weaknesses of the shoulders.
• cast shell on your characters.
• attack the shoulders with their elemental weakness.
• when they're gone, the boss will have a lower stagger threashold and take more damage.
• switch to synergist and sabertour, he is vulnerable to slow, makes things easier, you will also benefit from shell.
• when he charges for his insane attack, relentless assault, if you don't damage him enough he WILL one-hit kill you.
• Damage him enough and the damage will go down to about half.
• sentinel, medic, medic for quick recharge.
• continue stagger.

 If you're good you can get him down in just over 5 minutes. Most people do it in around 12.  He IS hard, don't feel bad about it.  I reccommend using lightning, fang and hope. "

Seems crazy to me that people are having so much trouble with this guy. I took him out first try. My advice would be to take electrosol right before you fight to get a shit load of buffs that can last the whole fight if you do it right. Defiantly take out all 4 shoulders and make sure you have a good healer paradigm to recover after his mega attack and you should be set.

I'm having problems with Barthandelus second form in chapter 11.  I can't kill him fast enough and get DOOM which kills me.

Finally beat this guy tonight.  Thanks for the tips guys.