Which Boss? I've been playing that game with my son. I like the way they did the villains section.
I like it better than lego Indiana jones and lego star wars but that may be because I've played lego star wars way too much due to my son.
I figured it out. it was the scarecrow plane battle. you have to stop his plane with the bat copter and then switch to the batplane and lob a missle up his tailpipe.
I really don't like some of the hidden parts because they really don't make it clearn where anything is.