Some of the best monsters are people. And some of the most intriguing people are villains.
Jon Wilson, of Appendix M put the bug in my head to steal a villain with his post on The Rival Party. These characters are decidedly different, with incredibly cool powers and abilities. I love the idea of a rival party as adversaries.
I immediately thought of a character I want to steal for a campaign. He is the Monomach from Stephen R. Donaldson's Mordant's Need series.
The Monomach is the villain's right-hand man, the most skilled swordsman in the land. As a villain, he is totally one-dimensional. He's given a target and then the target dies. Or at least that is how he should work.
He is actually simple enough to build an AD&D character class with little adaption. First, he is a fighting man so he has all of the abilities of a Fighter. Second, he has the disguise abilities of an Assassin. Third, he has some ability to heal himself like a Paladin. Finally, he will gain the damage bonus of a Monk. His prime requisites are Strength, Constitution, and Intelligence. To get a +5% bonus to exp, he must have at least a 12 in each of those skills. To get a 10% bonus, he must have a 15 in each.
In framing the villain as a character with a class, he can scale with the Player Characters. He can start relatively weak with the PCs and grow from there.
Let's assign those abilities by level.
On creation - +1 to Strength or Constitution regardless of race.
Level 1 - Disguise as an equal-level Assassin.
Level 3 - Laying has as Paladin of equal level.
Level 5 - Damage adjustment as per Monks +1 per 2 levels.
What are the Monomach character's limitations?
They are limited to two magic items plus one magic weapon and one magical piece of armor. They are limited to only equipment they can carry, even at home. They cannot backstab as Assassins do. They do not fight weaponless as Monks do. They do not have the variety of weapons of a fighter, they tend to stick to one main weapon and one backup. They don't often use bows. They can ride horses, but can not care for them. They work alone and are likely to strike at "friendlies" as they get in the way like a berserker. This berserker tendency is not a special skill or ability, it is just a ruthless and bloody methodology. They are relatively poor in day-to-day skills, unable to cook, care for animals or hunt making them reliant on their master's staff for self-care.
This lack of people and daily living skills prevents them from having followers, retainers, or constructing a keep, tower, or another base of operation. When assigned to retainers by their master, they tend to follow the retainer until a target presents itself.
What would make this type of character too overpowered? A crystal ball and a ring of teleportation. Yeah, I would totally give my evil Monomach a ring and crystal ball.