Lowest level to beat Sephiroth?

Spehiroth is pretty much cake, so long as at least two of your characters have Ribbons. I routinely beat him in the low-to-mid 50s, just by having 3 ribbons, and making use of DeBarrier, Big Guard and Regen. His main threats are the status effects most of his attacks cause (most notably confusion) [Ribbon protects this], and the fact that Supernova takes off 15/16s of your current HP [this is what Regen is for].

Also note that he gets more powerful for each level 99 character you have. It's not really enoguh to make him more difficult than at level 55, but it would be a significant boost over having all your characters 90-98.

As for Final Attack, first you have to buy W-Summon, buy and use Omnislash, and kill Ultimate WEAPON. The third is pretty easy, just rather time consuming chasing him around for about a half-hour. The first two come down to getting the worst possible effects from the slots on the last two stages of Battle Square (that's where most of your BP come from). Ribbons help immensely, and an Added Effect=Hades pairing in your armor serves as a good backup in case your Accessory gets broken by the slots. Big Guard and Regen work wonders, and if you are late enoguh in the game, make sure to use the character's Ultimate Weapon and a Mystile for the rest of the equipment. MP Absorb linked with something like Deathblow or Master Command is also useful for keeping your MP high enoghu to recast Regen and Big Guard, and a leveled up DoubleCut materia gives you 4X Cut, which is really good.

The Special Battle in Battle Square (which is what you have to beat for the Final Attack materia) isn't really any different from the others, except that the enemies are stronger. And if you run into a Ghost Ship, use White Wind *on it* immediately to petrify it, or it can eject you from battle for an immediate loss.

I did it at level 59 once. Kind of a pain, though. ;)

And the best way to make it through the battle square is to avoid relying on materia, because it tends to "break" kind of frequently during the slots. Also, Ribbons (you can get them by defeating Tonberries) are immensely helpful.

4 minutes KH1 =D Lvl 87 i cant remeber how long it took to beet sephiroth on KH2 by fact ive purely beet him as quickly as and didnt think of to time my self =P yet i became into lvl ninety seven i might say approximately 10-15minutes?

Just power level your party somewhere and get them to lvl 99 and use strategy while fighting seph.

What game is this?