Acheron

Acheron is a villain from Season 6 whom Selina serves. He is voiced in Nickelodeon by Sam Riegel.

Overview
A dark wizard who studied black magic while on Earth. In order to become the greatest sorcerer in the Magical Universe, he created the Legendarium. But he couldn't control it and was trapped inside it. Now, he’s trying to break free with Selina's help.

Appearance
His outfit is similar to the Dark Witch outfits of the Trix, consisting of a hooded shirt with large hanging sleeves and trousers tucked in boots.

Season 6
After the Treants failed to take over Lynphea College, it is revealed that Selina is in fact working under the orders of a mysterious dark being called Acheron housed inside the Legendarium.

Trivia

 * According to Greek mythology, the Acheron is one of the five rivers of the Greek Underworld. The spirits of the dead had to cross the Acheron on a boat to enter the Underworld.