Ursula, Flotsam & Jetsam
HP :: 450 Exp :: 1000
Floatsam & Jetsam HP :: 60 Exp :: 150
This is a tricky battle. Do not bother with the two fish as they are nothing. Ursula has very high defense. The key to defeating her is the cauldron in the middle of the room. Have a few ethers in stock. Lock onto the cauldron and use as many Fire or Blizzard spells on it as possible. This will not only harm Ursula, but also also weaken her defenses, in which you can take advantage of, and start attacking her until her defense goes back up. Use your MP well. If you run out, use ethers or strike Flotsam or Jetsam to regain MP. Continue this strategy and you will win in no time.
HP :: 900 Exp :: 1500
This is the true battle. Ursula grew a bit as well. Cast Aero and Sora and the whole party as soon as possible, and try to keep it going throughout the battle. This will bounce the attacks off you back at Ursula and increase your defense. It also allows you to counterattack Ursula. Try to get in back of Ursula's head and attack her with chain of combos. This is easier said than done as she keeps facing Sora. If she starts to inhale use Mermaid Kick to swim away from her as fast as possible, because if she inhales you and bites you, it will cause lethal damage. When she raises her trident, run away from her again, as she is preparing for a devastating attack of lightning bolts that is easier to dodge from a distance. She also will charge and fire and energy beam at you. Use Mermaid Kick to avoid this, or swim up over her head, as she will not tilt he head up to hit you. After she is done firing it, attack her head in the brief moment that she is vulnerable, but be ready to take evasive action again. If this battle is still to tough for you, then put some megalixers in Donald and Goofy's slots to decrease the difficulty of the battle. After you defeat her you will receive the Crabclaw key chain for your efforts at the battle.