The Raven's blood grants those who are affected with it dark powers, but also twists their personality to be crueler and more selfish. Prolonged exposure ends with them turning into anthropomorphic crows and being completely under the control of the Raven himself like Mytho himself in Akt 24 which happens when Kraehe dipped his Heart Shards of love into the raven blood which corrupted him when that heart shard.returned to him in Akt 13. Eventually, when Rue's love for the Prince enables him to break free from the tainted heart shard. Mytho tried to fight back against the corruption but couldn’t.
Rue was given raven blood since she was a baby and it allowed her to become Princess Kraehe.
At the finale battle with the Raven. He turned many of the townfolk into Ravens with the Raven Blood but soon they were purified and turned back to normal at the end. After Siegfried ask Rue to come with him into his story as his princess, Rue claimed that the raven blood is still inside of her with Mytho said that he wonder if it in his veins as well but it's unknown if the blood is still inside of them.