A lot of MMORPG that have different classes normally have a feature where when you get to a certain level, you can choose an advanced class, which specializes in a certain forte relating to their main class. An example could be a Musketeer choosing to become a Sniper or a Gunslinger. A Sniper could learn skills that let them hit foes from farther away on bigger battle boards and keep themselves safe from enemies coming into close range, and a Gunslinger could specialize in using two guns, one in each hand. Here's some of the ideas I had


Juggernaut: Specializes in being a tank with high health, defense, and use of Heavy Armor
Marauder: Not as good at tanking as Juggernaut, but can still take hits while dealing some damage on its own


Assassin: Better at keeping themselves hidden, perhaps a damage bonus for attacking from behind or a Damage over time skill
Corsair: Moves quicker and deals more damage, along with powers that increase agility and dodging


Sniper: Better range, more barricade skills, high accuracy
Gunslinger: Better damage, more trap skills


Shaman: Stat decreasing skills are more effective, more area of effect skills
Necromancer: More summoning skills, health draining skills are more effective


Officer: Stat increasing skills are more effective, more damage
Medic: More healing skills, healing skills are more effective