As the name implies they are made using a mirror. Specifically, they are made from the reflection of whoever the spellcaster wants to copy. You need the physical form of this person or it won’t work, as the mirror captures a hint of their essence which is needed for the golem to be brought to life. Aside from their eyes(which have no life in them), mirror golems look exactly like the original, unless the golem is injured. When injured, it becomes even more obvious that they are made of glass as their form splinters like it. But golems aren’t necessarily evil, it depends on the spellcaster and their purpose. Golems have all the memories and personality traits of the original, but these can be altered to make them behave a certain way. They are typically created with a single purpose in mind, and they will use any means necessary to complete it. If they can not, they will shatter apart.