The Rope Snake is Duster's last thief tool obtainable. Whether it can be called a thief tool or not, however, is debatable.
 Use and Appearances
The Rope Snake is used by Duster to swing himself and others with him across small gaps. Examples include the broken floor in the Osohe Castle.
The Rope Snake is also capable of transporting the group far distances, though it causes the snake harm to it's jaw. In Chapter 5, the Rope Snake lost it's confidence when it wasn't able to hang onto the Masked Man's helicopter. He tries to regain his confidence by transporting the party to Tane Tane Island, but again fails at doing so. This time, the Rope Snake chooses to hide itself in a hole, telling the team that it will make it big one day, and he'll be the greatest Rope Snake ever.
The Rope Snake is later seen at the end of the game, speaking with the player, as is most of the other characters in the game.