Merval and Descant Brill are major antagonists in the Artemis Fowl series by Eoin Colfer. They are pixie twins who serve as Henchmen to Opal Koboi. They are often the cause for Opal's failure. They appear in The Opal Deception and The Time Paradox.
Mervall and Descant were twins, which was uncommon among the fairy people. Because of this, they wee moderately famous, and appeared on several talk shows. At some point, they started working for Opal Koboi. She promised them that when she took over the world, they would receive Barbados.
The Opal Deception
When Opal was arrested, she faked a coma and was sent to J. Argon's institute. The Brill brothers grew a clone of Opal and in the meantime, started working for J. Argon as janitors. When the clone was finished growing, they smuggled Opal out of the clinic and replaced her with a clone.
They helped Opal with her plan for revenge, First, they put a bomb in a painting Artemis was trying to steal. They also helped her murder Julius Root. They got a surgeon to help Opal disguise herself as a human.
The Brill brothers helped Opal capture Artemis, and trap them in a park filled with trolls. While serving Opal, they were forced to obey ridiculous rules, such as not looking at her directly, bowing in her presence, not touching her food when preparing it, and not passing wind around her. She told them she could read their minds, but Mervall tested this by thinking that Holly Short was prettier than her.
They were part of Opal's plan to help the humans find Haven by sending a probe inside of molten iron to the center of the earth. However, to do this, they needed to set off bombs to direct the probe to Haven. The Brill Brothers stupidly left the bombs in one place, allowing Mulch to hide them. Artemis tricked Opal into setting off the bombs in her own ship. Opal, before escaping, betrayed the Brill brothers by leaving them to be arrested by the LEP.
The Time Paradox
Several years earlier, the Brill brothers were helping Opal gather endangered species to increase her power. They helped her caputre Artemis when he stumbled across the lab, (though at that point they didn't know who Artemis was). Opal locked Descant in a cage with a wild boar when he forgot to compliment her new boots. Opal thought Descant had a crush on her, and told Mervall that she would have to kill Descant if he persisted. Mervall tried to drain Artemis's brain fluid, but he escaped. Artemis released all of the animals and went back to the future. Opal, along with the Brill brothers, followed Artemis and Holly, but were too late to stop them. Opal erased the memories of the Brill brothers before following Artemis and Holly into the future.