He can be found in many towns such as Armadillo, Blackwater, and Thieves' Landing and he will likely be one of the first people that Marston will duel in the game. He can also be seen in the wilderness where he will challenge Marston to a sharpshooting contest.
In Undead Nightmare, Clifton can be found defending the monastery of Las Hermanas where he is usually on the roof of the main entrance. He often appears to be the leader of the survivors. If Las Hermanas is saved and Clifton survives, he will wander around the monastery grounds.
He can also be found during a random encounter, in which he claims to be sick and needs a doctor. He will then turn into an undead and attempt to attack the player.
How 'bout I make you famous? All you gotta do is agree to a duel.