Not every horror willingly submitted themselves to the rule of the Bogeymen and his Parliament of Shadows. Called the Thirty-first House--in reference to the thirty loyalist houses which compose the Parliament--these rebel horrors rarely possessed any real kind of organization. Instead, they would hunt humanity as horrors had done for millenia before, leaving corpses and legends of wicked monsters in their wake. They see themselves as the true horrors, unlike those soft souls who scurry about in their towns and citadels, emulating their human prey.
The Thirty-First House gets its name from a popular myth among the horrors. The story states that there were 31 elder horrors who swore allegiance to the Bogeyman during his rise to power. However, after the Bogeyman vanished in the 9th century AD, the infighting among the various factions lead to at least one house being completely destroyed. The Parliament insists this is not the case, and there have only ever been thirty loyalist houses, and most horrors accept that. However, in old records and ruins from the time of the Bogeyman's rise, there are occasional references to 31 houses...
There is no real leadership structure in the Thirty-First House--every member is generally left up to do their own thing, and live their own lives. They support each other when convenient, and generally try to avoid infighting. While some cells of the Thirty-First House do have established leadership, most members chafe under such constraints, and prefer operating as lone wolves.
Many members of the Thirty-First house believe the rule of the Parliament is making horrors "soft" and "civilized"--taking the monster out of the things that go bump in the night. They try to correct this by staging terrorist attacks, both on the Parliament and on other targets across the world--often with the intent of spreading as much fear as possible. The Thirty-First house has no qualms with killing humans, and will happily engage in a mass slaughter both for feeding and for making a political statement. Many of the other races attribute the acts of the Thirty-First House to horrors as a whole, giving horrorkind a reputation as savage monsters with no regard for others.