Because any guys who aren't supposed to be there replace your party members.
Sora can do the reaction command in Final Mix. With Glide and Combo Master, I was able to touch them. The "mountain" is just an image of a dark cloud. The Castle That Never Was is also an image, and Kingdom Hearts is a polygon model.
The character video leaves out Setzer. For him, you have to fight him in the Struggle after beating Hayner ten times as Sora.
