As with the other bosses in this game, there is no set pattern you can follow, so you need to be on your toes.
This boss will mostly be swinging from a rope, back and forth across the screen. He will also alternate between firing at you with the standard gun and the heavy bullet gun as well. (Standard when standing on the ground, heavy bullet when hanging from the rope.)
There is a timer that dictates when worms will pop out of his food and start crawling around. If one has not popped out recently, DO NOT RISK IT. Wait until one pops out, then cross where the pot is.
A lot of this is luck, but I had the most luck by finding a spot where he can't hit you with heavy bullets and just go prone, as the standard bullets can't hit you if you're prone either.
Keep trying, eventually you will get a decent streak where he just wants to get shot by you.
Good luck, have fun!