Corruption Index
A Corruption Index is a gauge measuring how many power rituals a planar outsider, such as a fiend or celestial has employed, regardless of success. Even if the power ritual is a failure, the entity is further bound to the demiplane of Ravenloft. In addition to their corruption index increasing, their reality wrinkle is shrunk even further, greatly reducing a entity's already limited power over the land in a gamble for a land-based power. Escape from Ravenloft is already difficult enough, and even one use of this ritual is enough to imprison an outsider for good.
Elsepeth and the Whistling Fiend are two such examples of fiends with high corruption indexes. Other fiends, most notably Drigor; as well as Inajira and presumably Styrix are wise to the uneven tradeoff to the land; and anticipating their own escapes have not succumbed to such a temptation. Drigor has expounded on this very thing in detail in his writings in the Madrigorian.
