This might sound somewhat crazy, but I think when master xehanort was talking about " that man is a monster infused with darkness", I think he was talking about terra. I the reason terra looks so much like the xehanort fro khII is because he is him and I think the darkness overpowered him, like at the end of the bbs trailer when his eyes glowed bright yellow. This will sound really crazy but, I think when terra was overcome by the drakness, he stole master xehanorts name, I mean think about it, when xehanort from khII went to far with the darkness he stole ansem the wise's name. Anyway just a theory