Marienburg is the underdog in long campaigns where their 100gc wear off and they have little real staying power. How about giving them a special skill list?
MERCANTILE GUILD SKILLS
Cloak and Dagger
The warrior has a habit of entering into sinister mercantile contracts.
Before each battle, secretly nominante 1 enemy hero. If this warrior takes that enemy hero out of action, he gains an additional +1 experience and D6 gc.
Working with the mercantile guilds, an elaborate forgery of a rivalling warband's orders is dispatched to an unsuspecting foe.
One enemy hired sword or henchman capable of gaining experience can do nothing for the first D3 turns of the game.
The Best Money Can Buy
Somehow, the warrior's equipment just always seems better in his hands.
At the start of each battle, warrior can choose one of the following:
(1) One weapon in the warriors possession that is not armour piercing gains the armour piercing special rule.
(2) One normal pistol in warriors possession becomes a duelling pistol for the remainder of the battle.
(3) Warriors armour save is 1 better than it actually is. Warrior must have an armour save to use this.
The innocuous merchants that the enemy warband was trading with before the battle were actually spying on the enemy warband for the upcomming battle.