Mest is actually a Council Member and Head of a Division of the Rune Knights. He's real name is Doranbolt. He was tasked to find any dirty secret from Fairy tail so they would have a reason to disband it. His magic is 'Memory Control' which he used to deceive the members of Fairy Tail into thinking that he is also a member of the guild.
posted over a year ago
He also uses teleport magic... Other than that good description :)