The Stump is a Town role and as such wins with the Town, regardless of previous faction.
There is no achievement for winning as a Stump, unlike other roles.
The Stump was a part of the 2013 April Fools Edition of -Mafia-. All people that are Watch-listed and above were instead Stump-Listed for the duration of the day. They were forced to be a Stump in every single game they joined.
It now has a semi-official status as a role - with the addition of the Auditor, the Stump can be a natural part of the game.