Devimon kept multiple wizarmon as servants in his fortress. They are loyal creatures who would obey his every command. They helped around the fortress, prepared food, and helped to raise Edward while he was younger. Now that he's matured, they obey his orders as well.
While Devimon and Edward were gone, the fortress was invaded by Icedevimon and his creation, Betsumon. Under the care of these monsters, they pretended to betray their previous masters and evolved into mystimon.