you chalange him to a dule but i remember you have to give him a neclace thing, i think it is on the ground after you beat the serpant snake

u have to challange the snake and u will find a pendant.
if u dont know how to get the snake out.i will tell u:
first u finish the musicans house in matataki and he will give a flute.then go to treant
the tree and get the serpent sword from him.and finally challenge the snake make sure ur
equip with the serpent sword before battling