According to Famitsu, when you change between Sora and Riku in Kingdom Hearts 3D is determined through the “Drop Gauge”. The “Drop Gauge” depletes over time, but it can also be drained manually. Once the “Drop Gauge” is empty, you’ll switch to the opposite character. You are also able to obtain temporary increases in powers for the incoming character, new commands, and items during the switch.
Famitsu also went into detail on the the Dream Eater creation process. Dream Eaters that are created through the recipe process (talked about here) can be made stronger using special items and you’ll even be able to give them names. The new “Ability Link System” will also allow you to use Link Points to unlock new abilities for your Dream Eater and for yourself. There are new screenshots after the break.