“We do not like to talk about the brotherhood, as there is something unnatural about consorting with evil in order to fight it. Yes, they remain anointed by the gods of light, but we find their methods suspect. Virtue should be enough. – Nalther Mytold, Paladin of Pelor.
The name of King An’essu’s youngest son has been erased from the records. Among those who study esoteric lore, he is known only as “The Corrupted King.” Over the course of a year, his father and four siblings all fell prey to poison, assassinations and demonic attacks. Newly crowned, he summoned his dukes for a ceremony to cement their fealty. The dukes were afraid that the king intended to compel them with fel magics, so they gathered together and plotted a way to protect themselves. Each of them went into the Worebel forest and killed a stag that had been tainted by demonic energies, eating its heart in a special ritual. Thus bolstered, they were able to resist the false king. The dukes did not keep their titles, as the people became as fearful of them as they had been of the usurper. They founded the Brotherhood as a way to make something out of what they came to see as a curse.
The Brotherhood does not recruit. Most often, they are approached by someone who wants revenge against an unholy foe and is willing to pay the price. Each brother uses his own judgement about whether or not to teach someone how to perform the ritual. The brothers have a mixed reputation. On the one hand, they are passionate about destroying evil. On the other, they give off an aura that makes people wonder if they might not be corrupt themselves.
Using the Brotherhood
I prefer not to flesh out my themes as much as Wizards does, because I want to leave them loose and abstract so that you can adapt them to your own purposes. In this case, the brotherhood is intended to have a feel where you get stronger, but at a cost. In your quest for vengeance, you’ve sacrificed something pure and clean. In my mind, the brothers creep people out.
Mechanically, the viability of the optional powers will vary on how often you encounter/include aberrations. I would be leery of changing it to any other origin, but if aberration doesn’t fit, changing it to a race/type would work in most cases.
Brotherhood of Inyetani Starting Feature
You lose one healing surge. You gain resist 5 poison and resist 5 necrotic. These bonuses increase to 10 at 11th level and 15 at 21st level. You can remove both the bonus and the penalty by vomiting up the stag’s heart (the magic of the ritual keeps it whole in your stomach), but you will need to spend an hour and 200 gold in magical reagents to reinstate them.
Brotherhood of Inyetani Level 5 Feature
You gain a +2 power bonus to Dungeoneering and Insight checks.
Brotherhood of Inyetani Level 10 Feature
You may make a saving throw against dominate and charm effects at the start of your turn, as well as at the end.