I cant kill the crawler. (The big canon)

Oh god, not that thing.. So far back....

Well, I had Tidus in there, Wakka, Auron, I just attacked the floating thing with Wakka and used haste on him to make it go way quiker. After you destroy the floating thing that disables magic, call some fully charged aeons, and use their overdrive, near the end just get everybody in so they get the AP. Not this hard eh?

First, make sure that everybody has an overdrive, including aeons. This is normally true of most bosses, but for this one, it's especially handy, especially if Yuna has an overdrive. You'll thank me later. Trust me.

Note that Auron just unlocked his second overdrive (Shooting Star)? That means he can get his third overdrive (Banishing Blade) as well. It is a long walk back, but very worth it. The following may be faster if you buy a sword with [First Strike] for Tidus at the shop, then use Flee with him for every battle to save time. Walk aaallllll the way back through Macalania forest (you may take a shortcut by taking the shining path) to the beginning. See that little bulb on the right? That's a Jecht Sphere, your second. Pick it up and watch it. Then, walk aaallllll the way back over the Thunder Plains, the south part. See that little bulb on the right? That, too, is a Jecht Sphere, your third. Pick it up, watch it and voila: Auron learned Banishing Blade. Practice it, it'll help a lot in future boss battles.

Now, for the actual battle. Auron does his Banishing Blade. Use Tidus to Haste first himself, then others. Use Wakka's Element Reels (aim for three yellow slots - Lightning) to take out Negator. Use Lulu for some Thunder or Thundara-fury (Thundara will do significant damage), use Rikku to steal. Kimahri just hacks away.

When you've done all that, have Yuna summon (not Grand Summon) Ixion. Note that Ixion is quite slow compared to Crawler, so time well. Ixion's Thor's Hammer will do anywhere from 7,000 to 9,999 damage to Crawler. Attack a few times, cast Thundara on yourself to heal, when Mana Beam is coming up, use Shield. Unleash Thor's Hammer and you've overkilled Crawler. Congratulations!

You'll thank me for having saved Yuna's Grand Summon later. Trust me...

quote Gotenks503

I had this problem a long time ago but...Dont destroy the Thing thats flying cause if you do everybody can do magic so mana beam is magic, ya? Then have yuna Auron and tidus out and dont for get what haste and cheer is for!

Haste will not work, since it's magic and guess what, that little flying thing (called Negator) blocks magic...

Also, do kill Negator. Yes, you get Mana Beam. So? An Aeon with Shield can take that and come on - he tells you three turns in advance he is going to use it.

With Negator out, it will be tough scoring an overkill on Crawler, since he is very resistant to physical attacks (it'll take ages to whittle him down with the boys, your physical attackers), and magical attacks (and aeons) don't work. There is a reason he has Negator out - Crawler is scared of 'em. So don't give him the advantage. Otherwise, the only thing I can think of that would reliably overkill (and you're not just going for 'a kill', right? ) Crawler would be Wakka's Attack Reels, and aim for three yellow slots. Doable, but I'd rather just start with this, get Negator out of the way and get to it. Thundara Fury away!

Kill it now or you will die
PS kill negator first or you will die trust it works