Imperial Insignia Guard is an esteemed unit of the imperial bodyguard. As many such units, there were two of them - Right and Left, of equal rank but with the Left being slightly more prestigious. A General (in this case Lang Bailing) is in charge of this guard unit. I might have to call it just Imperial Guards in the future if there isn’t enough space.

What’s translated as monster is actually yaoguai - a kind of spirit (usually evil, and almost always dangerous and feared) in Chinese folklore (notable examples can be found in classics like Journey to the West). Yaoguai are different from gods and demons and can appear in the mortal world. A lot of stories feature animals that managed to acquire some human characteristics and can talk, fight, etc.