The Illigom are an ancient, mysterious race. Some say they come from the Astral Sea (that's the Astral Plane for all those old cosmologists out there), while others say they have an extraplanar origin in some foreign Material Plane.
Whatever the case, hell follows the Illigom. They cause trouble. Some suspect the cataclysm that befell Duchy Aalsburg was caused by the Illigom, and according to rumor, the City Watch of Scandshar has standing orders to destroy any Illigom they witness within a mile of the city (some believe a couple of slave revolts in the City of Dread's history were organized by Illigom).
The Illigom are agents of change. A lot of the cosmologists in places like the Nentir Vale or the Sorrowfell Plains have abandoned the old Good vs. Evil / Law vs. Chaos cosmology (having adopted the World Axis cosmology in its stead), but no one doubts that the Illigom serve Chaos. Wherever they appear, they cause strife. They foster chaos and revolution wherever they appear. Frequently, their actions are subtle: they may heal a sick man, or place the proper words in the proper ear.
The aftermath is not subtle. Fires burn, heroes rise, kingdoms topple. Mao said, "Political power grows out of the barrel of a gun," and while that may very well be true, someone has to plant the seed of an idea first. The Illigom do just that.
Unsurprisingly, the Illigom are rarely encountered alone, although they are typically found with those whom they are courting rather than their own kind. (Equally unsurprisingly, Hereticwerks provided some inspiration for followers, if you find yourself out of ideas.)
The following specimen represents a typical Illigom, sowing discord and revolution among the local populace. In addition to its combat statistics, assume the Illigom Rabble-Rouser can cast rituals and achieve prophetic visions outside of combat, thusly allowing the creature to do what needs to be done. The Illigom Rabble-Rouser will attempt to keep distance between itself and its foes, opening with Opiate of the Masses to turn the tide of battle early in a conflict. It then uses Feeblemind when it is available and Lance of Faith when it is not. In melee combat, it prefers to use Bite so that it may escape its dazed opponent, typically resorting to its Quarterstaff if the target is resistant to poison. It uses its minor action for Don't Mourn, Organize! whenever that power is available. When one of its allies becomes bloodied, it uses Cure Light Wounds as soon as it is able.
The Illigom fight intelligently, but will frequently accompany their comrades unto death as a show of solidarity. That, of course, assumes that the Illigom who started a revolution sticks around to await its end.