So, whenever the Dark Lord puts facial parts on monsters, they become hostile. Most are his minions, however some were so powerful they revolted against him (as the Darker Lord) so he abandoned them in New Lumos. The point is, not all monsters were CREATED by the Dark Lord completely, such as the Rock Moths and Griffins, which are both seen in a docile state when not influenced by the Dark Lord's magic. They presumably were/are normal creatures in Miitopia before the Dark Lord attacked. Even Dominic is completely normal after you free him, and is OBVIOUSLY not one of the Dark Lord's original creations. However, in Karkaton, the Great Sage says something along the lines of "The Dark Lord makes many monsters, but those monsters are just weak creatrures. They're incomplete." and THEN mentions how he uses the faces to make up for that. This means that there are monsters the Dark Lord creates HIMSELF and THEN adds facial parts to. While not confirmed, I believe that the imps are some of the Dark Lord's original creations, given their resemblance to him and their association with dark magic, plus the fact that without facial parts have a blank slate where a face SHOULD go. I believe the same about the demons as well. Many of the others are up for debate though. Did he create the goblins? The banshees? What monsters do YOU think the Dark Lord created, and which ones he simply hijacked and turned evil?