So, you need to do the following, first, go left left right left, there, you will meet this dude known as ???, presuming you have the axe, then go to the monke HQ(Right Left Left Left), then go to the shack. Once you are in battle, then you can use the magic axe to kill ???. Once you kill it, you gain a shard. With the shard, you can kill Rick Gastly(kill weed man then go to abandoned shack's basement)