Data fights: with links included

Utawarezen, two versions per fight:
YouTube - Broadcast Yourself.
Apulapul2000, low level and no damage:
YouTube - Broadcast Yourself.

Xemnas I, Sora: all he does is more damage, and reverts to a dark glowing orb that homes in on you, otherwise, similar to the original fight

Xemnas II, Sora/Riku: he uses new attacks, and does more damage, but most of the time, he attacks by launching two orbs that deal continuous damage, otherwise, much less annoying

Xigbar, Party: identical to story encounter, except he uses the Japanese Sniper vision, which is way cooler

Xaldin, Party: does not use his spear dragon quite as often, Aero lasts longer and can only be broken by Jump, otherwise identical

Vexen, Party: is capable of creating clones of Sora, up to five (identical to Anti-Form), freezing Sora, and blocking the screen with Blizzards

Lexaeus, Party: it's over nine thousand and deals mostly one hit knockouts, uses the enviornment to own Sora id new and exciting ways depending on his Power level, which remains over nine thousand the entire fight

Zexion, Party: at first, traps Sora and the party in his book, where he begings to pummel you with miasmic visions of death and pages, even replacing your command menu; to be defeated, you must find and attack his book, and escape to Destiny Islands, where he can be damaged

Demon Boy VII, Party: same as before, but his Berserk is harder to dispel, because the claymores disappear unless you are right next to them to use them

Axel, Sora: identical to the second Roxas fight

Demyx, Party: Wisdom Form + Fire 3 is win

Luxord, Sora: identical to the story encounter, but draining his time is much more difficult, and if you fail the "get 4 O commands," you will lose Time, and add to his; fortunately, Time does not gradually drain

Marluxia, Party: has a counter over your head based on your level, equivalent to how many actual hits you can take before dying (he will rarely damage your HP); has two Reactions, one that deals a large amount of damage, and one that restores the counter by a few points; can turn the battlefield into a poisonous hole of death that deals counter and HP damage, turns into a car-like thing that chases you down, and turning the places where you step into fountains of death

Larxene, Party: very fast, very strong, likes combos and creating clones of herself

Roxas, Sora: identical to the story encounter, not that any of us have played it; fights like Sora, except better (if you suck, that is); after half HP, he begins creating beams of light that attack in a straight line, and uses the same Reaction command as Samurai, if you actually are in his path while he is attacking you (extremely quick version of the Samurai)