Quote Originally Posted by Tavrobel
You'll be fine if you spam Donald's Limit (Duck Flare/Comet, whatever it's called), or if you memorize Demyx's movements. Get through that part of the battle. The hardest part is the kill 10 in 10 seconds. The key is to use Wild Dance ONCE, and kill off the rest of the forms manually (Keyblade, they only have 1 HP).
Not really. Wild Dance is definitely more useful than Donald's Limits. The 10 forms in 10 seconds becomes 10 in 5 in Proud Mode. Following Demyx and attacking him after his waterslide attack (within the geyser barrier) and pounding on him relentlessly with an Explosion finisher is a pretty good way to drop his healthbars to the point he may never be able to use the Water Forms attack. Also remove any other combo+ and air combo+ attacks you may have. It's harder to beat the Water Forms when you have a slew of attacks before you finisher. They also do too little damage to warrant their use in battle.
Turn off Auto-Limit, but turn on Auto-Valor/Wisdom, incase you need the quick heal provided.
Not a good idea either. If you've used any other form too many times, you'll constantly end up stuck with Anti-Form which you cannot cancel.
His Rave attack SHOULD kill you; it does 2.5x damage. The way to stop Rave, is the Reaction Command, Showstealer, which returns the damage, and stuns him for a short time.
It's hard to time if you're not paying attention but it's real inconvenient to lose the battle because of this. Keep in mind, if you're too far away, he won't be able to manage the Rave attack at all.
The easiest way to kill Demyx is Anti Form. Too bad you have to have some good luck (or lack of it). Valor and Wisdom provide a free Heal, so use if necessary.
I don't think so. You're attacks are too long to deliver finishing blows to the Water Forms and you take too much damage and cannot heal. So you may find yourself just running away.

I had too many uses with the other forms and ended up stuck with Anti every time I tried to Drive during battle. I went Wisdom before entering the battle and used Sora's non-stop sliding Firaga to quickly dispatch the 50. I then cancelled the form so I could use my Explosion finisher against Demyx (Finishing Plus is also useful), following him through his geysers to attack him before he could move again.

Get as close as possible and get behind him if he starts shooting water balls. There's really no advice I can give about the water from the sky. You can run away, but it might hit you anyway.

Don't equip Guard. Do equip Retaliating Slash.