The Duelists

It's Raider courtship season, and for some reason one of the women, Yenkcha, has been smitten with Lieutenant Morgan. Jealous boyfriends and those eager to prove themselves have come knocking to challenge Morgan to a duel for the right to date. Morgan, of course, is too drunk to really care. Players may appreciate it, as these battles will all yield Skulls for you. You only get control of Morgan (and in one battle, Floyd), during the duels, but that's OK, because Morgan's handgun and Floyd's tranquilizer can easily neutralize the Raider duelists.
The first mission in this chain becomes available after completing the Raiderlands campaign mission.

The Duelists
Accept the Raider's Challenge!
Reward: 650 XP, and the fight will yield one Skull.
Next Mission: The Duelists 2: Cannoneer Run

The Duelists 2: Cannoneer Run
Accept the Raider's Challenge!
Reward: 650 XP, and the fight will yield one Skull.
Next Mission: The Duelists 3: I <3 Explosions

The Duelists 3: I <3 Explosions
Accept the Raider's Challenge!
Note: In this battle, Morgan tells the duelist that Floyd is the one the jealous Raider is looking for. Consequently, you take control of Floyd in this one particular battle.
Reward: 750 XP, and the fight will yield one Skull
Next Mission: The Duelists 4: Duel 4 Love

The Duelists 4: Duel 4 Love
Accept the Raider's Challenge
Reward: 750 XP, and the fight will yield one Skull
Next Mission: The Duelists 5: The Dream Child

The Duelists 5: The Dream Child
Accept the Raider Duelist's Challenge
Reward: 1000 XP, and the fight will yield one skull.
Next Mission: The Duelists 6: The Dream Child Part 2

The Duelists 6: The Dream Child 2
Accept the Raider's Challenge
Reward: 950 XP, and the fight will yield one Skull
Next Mission: Do You Remember Love?

Do You Remember Love?
"Stabbing? Seriously? Who brings a knife to a gun fight and then is still really scary? It's weird."
— Lt. Morgan
Available at Level ?. Added in 2.1 Patch
Accept the Raider's Challenge
The Raider Duelist is now a Raider Dustwalker.
Reward: 1,150 XP
Next Mission: Hate is Enough

Hate is Enough
Available at Level ?. Added in 2.1 Patch. This mission appears after some time after Do You Remember Love?.
Accept the Raider's Challenge
The Raider Duelist is now Sarin (300 HP). Sarin must be defeated in order to complete this mission, and despite holding back, per Yenkcha's request, Sarin is still favored to win. This battle requires a lot of luck, mainly Sarin not landing any critical hits. Tip: Use the BASIC attack then 2nd attack for Morgan.
Reward: 1,300 XP
Next Mission: Season of the Punch in the Face

Season of the Punch in the Face
Available at level ?. Added in 2.1 Patch. Available for some time after beating the mission above.
Accept the Raider's Challenge
The Raider Duelist is a Brawler (225 HP) who must be defeated. This battle also requires some luck in that the Brawler hits land randomly and can crit.
Reward: 1,350 XP
Next Mission: ??