I'll do my best to clear everything up.
Sora and Riku's MoM exam takes place in the Realm of Sleep. After the Blank Points ending, Riku is revealed to have cut his hair back to it's normal way (KH1). Once in Traverse Town (RoS), The two get new clothes based on their KH1/KH2 attire. The cast from The World Ends With You appear as well, making them the first Non FF/Disney characters to come into the series. Worlds that have been revealed are:
La Cité des Cloches (Hunchback of Notre Dame)
Country of the Musketeers (Three Musketeers movie)
Tron Legacy world
Prankster's Paradise (Phinoccihio)
Members of Org XIII have return as their Somebodies as well as Axel/ Lea.Vanitas has return as well along with Xehanort as Ansem SOD and his younger self. And Replica/Data Riku return as well.
Oh and Dream Eaters.
If there's something important facts I missed, someone tell me