This anchor is the point of connection between the Omega and the essence of death that they take. The anchor also prevents the Omega from being overwhelmed by the death essence. He used one of his horns because it is a manifestation of his divine ability. The horn contains some law fragments of the law of Slaughter so it is a very good anchor for the death essence.
The law of Slaughter is the orthodox law that empowers through killing. So using his horn allowed the efficient extraction of death essence. In other words, he gets more power from each dead thing. It goes well with the fact that he doesn't have a limit on the amount of death essence that he can handle.
He felt the changes to his body and commented silently, "It added less than 0.5% boost."
He shook his head. "It is too little. But little at a time makes big."
