This first part on the Land of Dragons is also easy. You'll meet Mulan and Mushu, and she'll tell you that she wants to enter the army in order not to disonor her family, just like the movie, of course. You'll go talk to Chang, and he won't want to have Mulan, which is called Ping for now, in the army. You'll try to make him accept her, and for that purpose, you'll have to do four missions, killing heartless. The battles in this world have a particularity: there's a gauge, of the party's morale, that you can't let run off. Every enemy you defeat drops special orbs, to increase the morale, and every time you're hit you lose orbs.
There are some new heartless, no big deal, but one of them a huge centaurus with a big lancet, can be a little tough, because he gives some strong attacks. You have to wait for the right moment to hit him. Anyway, on your fourth mission, you'll have to go to the mountain summit, fighting on the way there. You'll reach a little village, and Mushu will say he saw the enemy, Shan Yu, in a cave. You'll go there, hoping to defeat him alone, and by doing so, gain Chang's confiance. But he set you a trap, and you'll have to fight more heartless, only Sora and Ping.
When you finish, Shan Yu will have burned the village, and injured Chang. You'll have to go after him, and fight a ton of heartless he will summon, in the summit. you have only limited time, so focus on the big ones, who give more exp. Then a long cutscene will follow, when Mulan provokes a avalanche to bury Shan Yu in snow. Mushu will give away Mulan's secret, and Chang will expel them from the army. After, they will see that Shan Yu did not die, and he is going to the imperial city. You go after him, and it's the boss battle.
You'll have to protect the gates, while defeating Shan Yu. Kill the three heartless he will summon, and then focus on him. keep him away from the gates, and when he start to glow with a purple aura, stay away. use the reaction command whenever you can. It should be a easy battle, and after you finish him, the emperor will thank Mulan for saving him, just like in the movie, and the sword of the defeated enemy will become the key to open the route. You'll also get a new keyblade, Hidden dragon, but it's weak, so I suggest you stick with the regular one, or switch to the Star seeker.
After that, the ship will move on it's own towards Hollow Bastion. It's no big deal, merlin has found Pooh's storybook and wants you to take a look. I particulary hate Pooh's part, it's really boring and meaningless. You enter the book, but while you are inside, heartless attacks Donald and Goofy. You go out, and they steal the pages, so you'll have to go after them, just like in the first game. A brief battle occurs. Merlin is kinda mad because you didn't wait for him to come back with Squall before you entered the book. you enter again, and find out that pooh has lost his memory. It'll come back to him when you get the pages back, Merlin says. He gives you your first summon: Chicken Little (kinda useless). Now, you're all set, and have to go on to the only available world: The Olimpus Coliseum.