To my understanding it seems as though you run so far at first because he (the boss) keeps running after you. I assume you have that distance to run and turn real quick to strike. I'm not sure what happens if you reach the beginning, I didnt need that much space.
He seems to only take damage in the head, face area. He'll jump after you and stop every once in a while. I had to just run from him and when I had the chance turn, jump and hit him in the face. I didnt have any extra stuff, though the thing that makes your whip longer would have made it alot easier. A bit tricky as, with everything in the game, one hit kills you but be patient, you have allot of room to run backwards.
The game ends. I don't want to ruin for you but... You rule the land as you put an end to evil!
Hope that was helpful!
(btw I played it on my Lynx. I dont know how other versions are)