||Well, it's a really long time since I played KH2FM for the last time (I don't have a PS3 XD ) then I don't know exactly how I used to beat them, but I already beat everyone aside Xemnas and the Lingering Will in lv1, so I think I can help. One thing I learned that allies for every boss: Make your combo the normal length. No combo pluses. Finishers normally can help you a lot in a battle.
- For Demyx:I remembered of 2 different tactics I used, but don't know which one ended up being most useful. One is the Wisdom Form + Ether + Firaga, but with MP Charge disabled for it, then when Firaga is unusable, use an Ether, which would reduce the use of Ethers and make the reload quicker. At the same time, equipping one Negative Combo and Fenrir, and using all Finishing Plus available would make Firaga most useful, since we will use more Finishers, which affect a wider area, with less MP. If needed, you can also attack with normal Sora, since Explosion will defeat a lot of forms. Try to finish at least the first challenge this way.
- For Luxord: The trick here is not luck, it's timing. You need to get it very well, so you always win the clashes. For example, in the one he keeps 4 cards in front of you and change where's the circle (the only one I remember, in fact), I wait a the speed to drop down a little then choose the second command and once the circle shows up in the last card I use it. But you don't need to use this. Just Glide far from him and he will nor hit you, nor transform you. If you end up trasformed, hitting him with a jump will reduce your Drive bar quicker. AFter his card attack 2 hit combo, he is open for attacks. Also, try to hit him with an Aerial Combo when he jumps after summoning two cards. To destroy them use Reflega when they are near. You can also wait for him to jump to you after he summons the card, use Reflega to defend from them, nad the magic will hit him too when he gets near. When he transforms into a lot of cards, pay attention to which is him. If you're not sure, turn the camera around to the right, in the contrary way of the moving cards, so you can see their front. AFter releasing him, he's open for more attacks. For his desperation attack, use Aerial Dodge + Glide, always locking on to him to see where he is. For the final clash, which is needed to win, it changes between circle and cross consecutivelly, rising the speed with each correct command you achieve. Again, timing. You must try a lot until you get it. After you win it, just cast a Blizzaga from the distance to do not get hit.
And for the Mushrooms, which are impossible to beat at lv1. You will see that I used Wisdom Form a lot here XD :
- For Nº 1: Timing + Wisdom Form with Negative Combo and Fenrir.
- For Nº 3: Along with the strategy Kryten said, try to use Master Form. It runs kinda quick and his Aerial Dodge travel a great distance and if you predict the Mushroom, you can dodge just at his back, getting everything he drops. If this doesn't work, try Aerial Dodge with Sora instead of Gliding.
- For Nº 6: Well, I use each of the magics according to the situation. I use Final Form or Sora not transformed. If there are copies is in a horizontal line, I use Blizzaga on the start of it. If there are vertical lines, I use Thundaga. The ones that appear in a V like formation near the wall, I use Thundaga too. The ones in circle, either Firaga or Thundaga. Ethers are highly needed.
- For Nº 7: Final Form + Reflega and at the end Blizzaga. Equip Your mst powerful Magic Keyblades, such as Ultima Weapon and Fatal Crest.
- For Nº 8: Had a lot of problem with this. Porbably used Wisdom Form with Negative Combo too. Keep the right distance for the shots to connect. Mantain the distance. You can also try Berserk Charge, instead of Negative Combo, and use Curaga as soon as the bar fills up. Or try the Thundaga tactic, which I sadly never tought of :(
- For Nº 11: I use Wisdom Form, with Negative Combo and Fenrir and Finishing Plus. Wisdom's Finisher launches a barrage of shots that can potentially deal a lot of hits. You need to get the timing of his jumps to get farter or closer to him for the hits to connect. If he is on the ground, get very close for the hits to connect quickly. Tested this just now, 80% chance to win easily.
EDIT: Revived my PS2 and tested some of those tactics. Luxord and Demyx are good ones, just beat them in the same conditions you are. Mushrooms, only tested Nº 11 and Nº 7. Don't remember how to finish Character Links, sorry :(