The three magisters, consisting of magisters Vax, Ando, and an unnamed third, are presumably devil binders in the Void. They were first seen offering to replace the mask of a crimson devil. They have relatively weak wills, so their shades appear withered.
They make use of ley-stones instead of Keys of Kings. They noticed that Allison had a Key of Kings and presumed her an Emissary. They seek employment as Emissaries of one of The Seven, but were put off of the idea when Allison lied that she worked for Mottom.
They have the audacity to think that knowing what they are doing is the path to success. The magisters were left by Earth's Door after the deal with Princess Mamoru Moonshine Jagermeister Jack Jack Daniels Timothy Tim Bill Freddy Mercury Blueberry Luna, Esquire.