you have to complete the house first for the "happy" looking dude who plays a banjo looking thing, when it is complete and the "event" thing comes up go talk to him....he will give u a flute that will summon the "snake"
You must have the serpent sword that "treant"(the tree with the eyes) gives to you, so go talk to him.

okay here is what you do is complte the minstrels house in mataki village!then he will give you a little flute thingy that will summon the snake(only beacause it sounds like a mouse!)but to beat him you need a special sowrd called the serpent slayer! you have to reconect the river to him then he will come back to life!but u cant understand him so get the hunter earings that u found and put them on! now u can understand him and he will award u with the serpent sword! its your only hope in beating the snake! good luck!

i am talking about trent the talking tree! srry!u have a to reconnect the river to him and he will give u the sword!!!!but u need t hunter earings to understand him!again this is all about trent!