When you go to the Haunted Masion for the last time as Roxas and after you talk to Namine before Diz takes her away, when you go into the other room notice that roxas draws a symbol in the last ring on the table, you can't see what the symbol looks like, but in the other two, one is a heartless symbol, and the other is the nobodies symbol, so what was the 3rd that Roxas drew, i think this will come into play in khIII as maybe a new enemy