Kingdom Hearts: Chain of Memories/Riku/Atlantica

After clearing the room of Heartless, go to the north door and synthesize using a card with a value of 1 or more. Do the same in the next two rooms and you'll reach Room 4. After defeating all of the Heartless here, return to the second room. Strike the remaining door and synthesize using a card with a value of 1 or more. In the next two rooms, strike the doors and synthesize until you reach Room 7. Go to the north door and synthesize cards with a blue border. to make a value of 15 and the Key of Beginnings.

Ursula
Ursula, in a mimicking of events from Kingdom Hearts, grows into a much larger version of herself. This boss battle, unlike many of the others, shouldn't be very hard at all. Her attacks aren't very damaging but easy to dodge or card break anyway, and she doesn't move around much either. It'll be easy to stay on top of her by moving around a lot, which she quite obviously isn't capable. Card breaking is a breeze in this battle and even then, dodging also proves quite effective. As long as you're at the right level, which should be somewhere over 25, this boss will be a breath of fresh air. Ursula's attacks include: Once you defeat her and obtain the card she leaves behind, go back to Room 2 and follow the path up for two rooms. When you reach Room 10, go to the north door and synthesize using a card with a value of 1 or more. Go through the door in Room 11 to return to Castle Oblivion.
 * Quite simply, Ursula casts Thunder. This acts the same as any other Thunder attack, and can be avoided easily by card breaking.
 * Bubbles come for you and, along with taking away your health, will also confuse Riku. The controls will be messed around with and you'll have to work your way back to Ursula with your new control scheme before the confusion wears off.
 * A lightning strike is emitted from Ursula's mouth, so keep away when you see her preparing this one.