I'm sure there will be a walkthrough for this. Me? Luckily I did know how :
While you're at the upper part of the road, when he charges at you which you should not wait for him, move Larry downwards so that the boss will throw a spear on you. Yeap, later you grab the spear and throw at him back and he's stunned and you know what to do.
Beware, the Level 3 freak monster could have been much worse. I've been there and it's probably the most annoying boss I ever faced.
Luckily also that walkthroughs are available on Youtube. And if you think the freak boss is bad, use the frost or ice sword, once his attack slows down significantly (Don't count on the ice sword's damage), in this way, you can retreat easily when he swings his chopper knife compare to he's attacked normally.
Played with that ice sword is a lot easier but still have to bear with your energy as you still need to escape from him without locking yourself into a dead end.