Using the Horror rules in the Revised edition book, there are several things I integrated into DC T20 that I think works well with the setting.
Sanity and Fear
(True 20 Adventure Role-playing, Revised Edition, pg 224)
Use Fear and Terror as is in the rule book. Every creature and beasty has a Fear/Terror Rating equal to their total levels. The creature type determines the type of role as on page 227.
(True 20 Adventure Role-playing, Revised Edition, pg 230)
In Dark Conspiracy, the Dark Lords and the minions are out to corrupt the world with their evil, cause as much pain and suffering as possible and feed off of it all. In this effort, the Dark Lords recruit Igors. Igors are defined as humans that serve the Dark Minions. This could be knowingly or unknowingly. But where does free will go? Why do these people do the things they do we, willingly or unwillingly? This is where Corruption comes in. Serving the Dark Minions and doing their bidding earns levels of Corruption much in the same way as the deeds in the Core book explain.
However, in DC, the effects of Corruption is different. Each point of Corruption a character has acts as a penalty to Will saves against any power used by the Dark Minions. The more work the person does for the Dark Minion (knowingly or unknowingly), the more corrupt they get. The more corrupt they get, the harder it is going to be to resist their bidding.