The first time I beat him, I used nature form and made myself a little cactus fort to hide in. He keeps charging you and bouncing off the cactuses till he dies. It can be pretty hard to make a tent you dont slowly get ejected from though, but you can always make more. It felt like cheating though (and I somehow managed to die to one of those shooting mechanical crabs on the wasy to the save point) so I fought him again with nature form. I just ate 3 of that food that gives you ammo in beast form. spicy soup maybe? Then you can stay in beast form the whole time and just wail away at him. His 2nd form gets slightly harder, but if you are careful you wont have to heal once.