Kingsman Return

Shade Lord Kremlin

Corruption... this was one of the innate abilities that the Shade race possessed.

It was one of the ways in which they used to grow stronger naturally. By stimulating the hidden desires of living beings, the Shades are able to gradually integrate their own powers into the body of other living beings, making it so that body would be more compatible with their powers.

This kind of phenomenon is usually shown in the form of an exchange of power where the Shades led their own powers to others. Because of how invasive the nature of a Shade's power is, this exchange of power can lead to some irreversible mutations happening in the target's body.

This is how the fallen come about.

Those living beings that become fallen do so because they accepted the powers of the Shade, causing their bodies to go through such an irreversible mutation. As for how the shades would benefit from this kind of relationship, this is done because as a Shade lends his powers to another,