Shan-Yu is fast, but his attack power is relatively low. To begin, rush in and start attacking immediately, preferably in Valor Form. The Heartless will appear randomly and start attacking the gate. When this occurs, it is best to defeat them immediately since the protection of the gate is the main goal. It is advised that in order to keep the gate's defenses high, Sora should pick up the orbs dropped by the Heartless enemies so keep an eye on the damage gauge at the top of the screen.
A good way to defeat the enemies and Shan-Yu at the same time is to save Mulan's Limit, Red Rocket, until a point where Sora is up against both at the same time. When the Heartless are defeated, concentrate Sora's attacks on Shan-Yu.
Shan-Yu is most dangerous when he is pulsating with dark energy. Watch out for his Joust ability, which sends Sora across the arena, and an upward spiral attack. Both leave him open for attack followed by a combo. When prompted, use the Reaction Command to enter a grapple with Shan-Yu and inflict a lot of damage.
It is also wise to keep an eye out for Shan-Yu's pet falcon, Hayabusa, as it can easily pick Sora with its talons if it gets close. Locking on and attacking the falcon will take it out of the fight momentarily, though it will soon reappear. Attacking the falcon will also release restorative orbs if needed.
Remember to heal when necessary. If Sora is defeated during the battle, the option to play as King Mickey may appear. However, King Mickey should not be needed, and Shan-Yu should fall relatively easily.