I want to make the ender dragon and the wither fight, but when I try, the wither cannot hit the ender dragon, so the ender dragon is not interested in fighting. Is there a way I can make them fight each other?
Like @ghostwalker13 said, if you put invisible mobs that the other boss "hates", then they would shoot at each other. Other than that, without commands, I think standing on the side opposite to the Wither on the Ender Dragon would work. You could also change the code, just like you can change the number of blocks pistons can move. It's just a number in the code, just like (I assume) the mobs that each boss "hates" would just be a string. Also, it depends on which version you are using. In PE, you won't be able to do the command version, and on iOS it would be tedious to change the code. I haven't played any console version, so I don't know if it would work there. In PC, it's PERFECTLY possible. I don't see any reason that it won't work.