The Unlyncher is a third-party role whose objective is to prevent a specific player from being lynched. These protected players are called Unlynchees; the fact that they are Unlynchees is usually hidden from them.
If the Unlyncher dies before the Unlynchee, the Unlyncher can still win the game, but their fate is now out of their own hands.
If the Unlynchee is lynched, the Unlyncher loses and leaves the game.
The Unlynchee is almost always Town - otherwise, the Unlyncher almost necessarily wins with scum.
There is no consensus as to what happens if an Unlynchee is nightkilled.
Sometimes an Unlyncher will have more than one Unlynchee assigned to them. All of them must be protected. An Unlyncher with this kind of Win Condition will usually have some kind of protective ability to help stop night-kills that may fall on their Unlynchees.
Alternatively, an Unlyncher will be charged with making sure at least one of a group of Unlynchees survives to the end of the game.
Use and Power
This role has been criticized as being luck-based - drawing a VI player for an Unlynchee is horrible, while getting a particularly well-known player for an Unlynchee means the Unlyncher doesn't need to do anything.
Aside from being a setup-based protection on a certain player, it serves no purpose except a challenge.