Heres mine-

Spherimorph-
Hit the Spherimoroh using a physical attack.It'll counter attack with a spell.If you're lucky,It'll use fire or thunder.Lets say it used thunder.Summon Ixion and keep using physical attacks.The Spherimorph with cast thunder on Ixion,healing him,then it'll use its normal attack or press.You may as well turn off the tv screen,because it'll keep healing Ixion,then hurt him,then Ixion will attack.You can do this with Ifrit too.

Crawler-
In the Thunder plains,be sure to steal electro marbles and lighting marbles from enemies.Collect about 20 electros and 8 lighting.In the Crawler fight,have Rikku,Kimhari and Auron on the field.If you've done a fair bit of training,Kimhari should know Steal and Use,just like Rikku.Use those marbles on the crawler!DO NOT TOUCH THE NEGATOR!!!The electro marbles inflict 900 damage
each time you use them and the lighting ones inflict 1000+.Use Auron to attack the crawler.Using this strategy,I beat the Crawler in less than 4 minutes!

Hint for 1st Seymour fight-
Have Rikku,Yuan and Auron on the field.Summon Ifrit [He should
be in overdrive,if you used him in the Spherimorph fight.]Use his overdrive immedietly to overkill the Guado Guardians and take off more than half of Seymour's HP.When he summons Anima,keep Ifrit and keep using fira on himself.Eventually,he'll hit overdrive and you can slice off a fair bit of Animas hp.

Here's another-

Sancuatry Keeper

Use Auron's threaten and he wont do a thing fo for the rest of the battle!:)

Please don't add off topic/random attachments. Thank you.

I think the cheapest and easiest boss strategy is to build up both your character's overdrives and your aeons overdrive's beforehand, then just unlease them.

For a few of the first seymour fights all you need to do is cast reflect on him and your entire party. this only works in the bttles he doesn't attack you but instead uses magic. He'll kill himself while healing you.

Evrae Altana-

He has Zombie staus,so use two pheonix doens to kill him.

u dont really need any strategies if u level enough before the boss >.> i see many people asked about how to beat seymour 1 2 3. i never had problem killing seymour -_-a none of my party members die during the fight. all u need is auron, tidus, and yuna basically in most of boss fights. well yuna for her white magics not aeons. aeons are not needed if ur chars are strong. i never used aeons except for aeon duel and final battle.

As said before I find the easiest strategy is to put everyone in overdrive before the battle. Also make sure to equip armor that strengthens you (unless the boss can cause status affects easily). What I always found to be simple is after Bevelle to use Bahamuts overdrive and this defeats any boss easily, or takes away much of their HP. The second seymour I used Shiva first then Bahamut and he died instantly (though only Yuna gets most of the AP so let everyone take a hit first..)

Whenyou get don tonberry in the moster arena get 3 weapons with overdrive->ap and triple overdrive on. Then set 1 of your party members overdrive status to stoic and the other 2 to comrade. Have the stoic player attack the tonberry and everytime he will be hit with the counter attack karma wich will do 99999damage, keep reviving him with the other players and sending him back to fight. Olny have the stoic player attack. This way the amount of damage done to that player will be changed into AP after the fight, you can get millions of AP using this method also if you flee the battle before the tonberry is dead you still receive the AP.

haha i gave every sphere thing to tidus (strength +4, luck +2 or whatever) and when the end of the game got closer, tidus was doing 99,999 damage on regular attacks. on top of that, i constantly casted haste on boss battles and pretty much watched the battle beat itself. it really made the game too easy to beat though, so i only recommend it to people who cant beat the game for the life of em.

i know! buy a gameshark, turn the codes on, and fight;)

Seymour Natus:
Ignore mortibody and cast reflect on seymour, after doing this do not use any magic, (fire water blizzard etc.) on him, it will hurt you. if you choose to cast reflect on seymour keep hard hitters like Auron out. keep Yuna out for restorative spells on your players and rotate your third character between Tidus, Wakka and Kimahri... if you wish, use Rikku as well....... I would not recommend using Lulu in this fight at all, she has little uses besides magic. Seeing as the Mortibody will drain life from Seymour use only overdrives on it so that its HP runs low and it takes HP from Seymour, then keep attacking until another overdrive is built up.
Aeons are very useful in this battle as Seymour will only banish them the next turn he gets, so dont rely to much on them.

(When I fought Seymour Natus... I overkilled him with a regular attack from Auron, it only took me five minutes to beat him)

Strategy for Seymour Flux:
Step 1. Get all aeons into overdrive
Step 2. have Tidus, Auron, and Yuna out
Step 3.Cast reflect and Protect and Hastega on everyone
Step 4. Cast Bio and Reflect on Seymore
Step .5 Summon Aeon after Aeon Using Overdrive this should finish him off and target the overdrives mainly on seymore

Sanctuary Keeper:
Steps 1-5: Do everything in the above Strategy
Step 6: if its still alive smack it with melee attacks

Braskas Final Aeon
YOU MUST HAVE ALL CHARACTERS AND AEONS IN OVERDRIVE!!!

FIRST FORM,[60,000 HP]
Have Tidus Auron and Lulu out in that order.Have Tidus use
hastega on the party.Have Auron use Zombie attack and Lulu doublecast flare,ultima[You dont HAVE to have flare or ultima,I didnt have it] or level three magic on the aeon.The pagodas will deal 1500 damage to BFA because of it's Zombie status,then heal it by 1500.Have tidus cast haste on one pagoda and slow on the other.This will space out their turns.Have Auron use Zombie again.Bring out Yuna to use curaga on the boss.This should do about 5,550 damage.Now,have Tidus using Quick strike repeatedly.Have Auron using Zombie Strike or Power Break.You should kill the first form very easily doing this.

SECOND FORM,[120,000 HP]
Continue the same strategy,but have Auron only use power break and Yuna use Holy.When you feel that you've got off a good percentage of his hp,have Yuna summon Valefore.Use his energy blast to deal 9,999 or more.Continue until you get to Bahamut.When you use his overdrive,it should deal about 25,000 damage.Bahammut will get killed by the final aeon.Use your party mermbers to damage the aeon some more,then summon Anima,use her overdrive to deal more than 30,000 damage.I dont reccomend Yojimbo,he only attacks the pagodas.
Now summon the magus sister and combine powers for an awsome overdive,Delta Attack.This should deal ALOT!Dismiss them ASAP and summon them again in grand summon.Perform Delta Attack again.This will be an overkill.

OVERDIVE SIN

This is a toughie!Have Tidus cast hastega,lulu doublecast and Yuna or kimhari cate holy.Keep doing this until Sin comes close enough for melee attacks.Have Kimhari use Nova[Learned from Omega Weapon] and have Tidus and Auron use their over drives.Have Yuna summon all the aeons and use their overdrives.Bring out Anima[I only had herat the time,not Yojimbo or the Magus Sisters] and use her overdrive[scary].This should overkill Sin,since at this time,Tidus's attack should deal 8,000 +.If you have high luck,some of Aurons attacks will deal 9,999 damage!Don't let Sin cast giga gravitation or you're finished!

Omega Weapon.

I found this battle much easier than the crawler/negotor.Two words.Aeon Overdrives.Omega weapon never hurt my paty members because of aeons.Make sure you have Anima!When her overdrives used[should kill Omega] Omegas not overkilled,use pain and attack.This is a very easy fight.I reccomend fighting it after you defeat SAin's left and Right fins,Core and the final sinspawn.

everyone probably knows this but ne way

Yu Yevon black thing (the last final battle after u defeated all of the aeons)

-make sure kimari gets doom from a skelaton ghost in the calm lands gorge

-have kimari out and cast doom on it and it will be dead soon