What exactly is the definition of a monster? I mean the “big destructive creature” kind of monster, not the “really evil person” kind. I think it’s a little questionable whether it’s ever okay for a natural animal, even in a supernatural setting, to be portrayed as a “monster” in the sense of it being okay to kill it without considering other options; I can’t deny that I like some of the classic ones that don’t make much sense to be anything other than animals, but I’d prefer to make them more like, well, animals. For truly monstrous monsters, I’d go with demons or with artificial creatures, depending on the setting.
For Project Quintessence, the villain Ashroth relies partially on created monsters that aren’t even made of normal matter; the alien nature is probably why I made many of them tend to be otherworldly tentacled creatures, but some of them are dragonlike as well.