Ok. First off I've not actually completed this game yet, considering that when I start a new game to get my characters more leveled up because I know what to expect, the disc freezes at Mi'ihen Highroad. I'm getting a new disc soon enough but I've got this save data that is past the part where it always freezes. And that's the Mt. Gagazet Seymour Flux battle. I'll start by telling you stats and abilities of my characters cos I really need help TT_TT I now regret fleeing easy battles.
Tidus:

HP: 2420 MP: 112
Strength: 25 Agility: 22
Defence: 21 Luck: 18
Magic: 23 Evasion: 16
Magic Defence: 12 Accuracy: 17

Skills: -

Special Abilities: Steal, Use, Pray, Cheer, Jinx, Lancet, Provoke.

Wht Magic: Life, Scan.

Blk Magic: Fira, Thundara, Watera, Blizzara, Drain.

Lulu:

HP: 2604 MP: 212
Strength: 13 Agility: 25
Defence: 24 Luck: 17
Magic: 45 Evasion: 52
Magic Defence: 46 Accuracy: 10

Skills: Extract Mana.

Special Abilities: Steal, Use, Luck, Spare Change.

Wht Magic: Protect, Reflect, Dispel.

Blk Magic: Fire, Thunder, Water, Blizzard, Firaga, Thundaga, Waterga, Blizzaga, Demi.

Auron:

HP: 2630 MP: 153
Strength: 28 Agility: 17
Defence: 24 Luck: 17
Magic: 9 Evasion: 10
Magic Defence: 7 Accuracy: 11

Skills: Delay Attack, Power Break.

Special Abilities: Use, Luck, Provoke.

Wht Magic: Cura.

Blk Magic: -

Wakka:

HP: 1318 MP: 50
Strength: 19 Agility: 12
Defence: 14 Luck: 19
Magic: 28 Evasion: 5
Magic Defence: 15 Accuracy: 27

Skills: Dark Attack, Extract Ability.

Special Abilities: Steal, Use, Pray, Lancet, Guard.

Wht Magic: Cure, NulShock, NulTide, NulFrost, NulBlaze, Scan, Esuna, Life.

Blk Magic: Water, Blizzard.

Rikku:


HP: 1496 MP: 205
Strength: 16 Agility: 22
Defence: 15 Luck: 18
Magic: 15 Evasion: 8
Magic Defence: 8 Accuracy: 14

Skills: Delay Attack.

Special Abilities: Steal, Use, Provoke.

Wht Magic: -

Blk Magic: -

Yuna:

HP: 3123 MP: 204
Strength: 13 Agility: 24
Defence: 15 Luck: 17
Magic: 41 Evasion: 34
Magic Defence: 32 Accuracy: 10

Skills: Extract Ability.

Special Abilities: Steal, Use, Luck, Spare Change.

Wht Magic: Cure, Esuna, Reflect, Dispel, Scan.

Blk Magic: -

Kimahri:

HP: 1148 MP: 158
Strength: 20 Agility: 17
Defence: 19 Luck: 18
Magic: 34 Evasion: 17
Magic Defence: 15 Accuracy: 5

Skills: -

Special Abilities: Steal, Use, Lancet.

Wht Magic: Cura, Protect, Shell, Scan.

Blk Magic: -


Ok, I know Tidus doesn't have Haste/Hastega, and I know Lulu doesn't have Bio. Yes, their HP isn't as good as it should be at this point in the game, but I got through most of the game with them like this :( And I just wanted to get straight on with the game, I didn't expect a battle as annoying as this to pop up. Help me, please:(

Please post questions relating to particular games in the FF series under the appropriate forum. You can also search "Seymour Flux" under the search option to read previous posts for strategies and tips.

To answer your question, all you need to do is level up (to get higher stats and abilities) and get your aeons' overdrives full for when you summon them during the battle. If you can't be bothered with that, here are some alternate strategies to kill him quickly. For the first one, you do need Bio and Haste (courtesy of Split Infinity on Gamefaqs):


FIRST cast Haste on Seymour Flux, THEN Bio on him and then STOP ALL ATTACKS ON HIM. Wait 50 turns for him to do his actions - each will rip off 1400 of his health, including on turns he skips cos he got a turn in faster than Mortiorchis. During this time you mustn't do anything to him, not even Scan him. As soon as you do, bang! He'll start using Total Annihilation and Flare... but if you don't touch him at all, all you'll be seeing are Lance of Atrophy, Full-Life, Dispel and Cross Cleave.

For the second one, you only need Haste (courtesy of Siniroth X on Gamefaqs)


You must make sure that you have two Wings to Discovery in stock for this strategy to work effectively. What you wanna do first is cast Haste, Protect, and Shell just in case you cannot defeat Flux in *two* moves (wow, huh?). First have Rikku Mix 2 Wings to Discovery to get Trio of 9999. Now have Tidus use Slice & Dice, each of 6 hits will do 9999 damage to Flux and reduce him to mere 10000. Just have Auron use physical attack for 9999 and then have Rikku attack to finish it. Don't worry about Lance of Atrophy/Full-Life combo, ok? You win!

For the third one, you only need Haste (courtesy of Harry Macdougall)


Before the fight, get Auron's overdrive, Lulu's overdrive, and every Aeon's overdrive set and ready. Make sure Tidus has Haste.
1. Enter the battle with a party of Lulu, Tidus, and Yuna.
2. CAST HASTE ON YUNA!!!!!!!!!!!
3. Summon Valefor
4. Use Energy Ray
In between 4 & 5, Seymour uses banish, and the thing absorbs 4k from him.
5. If it is Lulu's turn, use Thundaga Fury. Make sure you get at least 6 of the twirl things done.
6. Switch Tidus for Auron if it is Tidus's turn. If not, summon Ifrit.
7. Use Hellfire
In between 7 & 8 Ifrit dies.
8. By now you should have Auron in, use Shooting Star.
9. Summon Ixion (Lulu and Auron shouldn't get many turns because of haste on Yuna)
10. Use Thor's Hammer
NOTE: Now the Mortiorchis should be steadily healing itself, and draining Seymour too.
11. Summon Shiva (for any of Auron & Lulu's turns, have them keep everyone healthy and happy)
12. Use Diamond Dust.
13. Summon Bahamut.
14. Use Mega Flare.
15. By now Seymour Flux should have about 500-1000 life left. He shouldn't have even used Flare yet. It may be Yuna's turn again. Switch to Tidus and attack. If he doesn't kill it, he should knock off a good chunk. Seymour should use Flare now. If it hits Auron you're fine. If Lulu dies, he may prep for Total Annihilation. If this happens....pray.
16. If you survive to Auron or Lulu's turn, have Auron attack or switch to Wakka for Lulu and attack. He should be dead.

Whoa, nice strategies in this forgotten thread, tks!!