Reasonably certain that they are dressed up as Ghostrick monsters. Here's what I identified:
Aluber: Ghostrick Alucard
Quem/Cartesia(?): Ghostrick Yuki-onna
Fleurdelis: Ghostrick Jiangshi
Dogmatika Adin, the Enlightened (The Golden Swordsoul): Ghostrick Mummy
Dogmatika Theo, the Iron Punch (The Golden Swordsoul): Ghostrick Stein
Shuraig: Ghostrick Ghoul
Ferrijit: Ghostrick Angel of Mischief (judging by hat)
Rugal: Ghostrick Warwolf (judging by collar)
Albaz: Ghostrick Nekomusume
Ecclesia: Ghostrick Specter
Kitt: I can't identify