To Be Left Alone?
Isolation isn’t desired by most, but if everyone thinks you’re hideous or evil, you probably don’t want company unless it’s other monsters, which raises the question of love between monsters (whether of different kinds or not). Is the monster being hunted simply because it’s been seen and is feared, or has it done something to stir up other species? Do any of our species think the monster has a right to live unmolested or does pretty much everyone want to kill it? Such conflict is good for stories and a debate on the right to life.
To Hoard Treasure?
This idea is often used but doesn’t make that much sense because treasure is no good when we can’t barter it for other things. By definition, monsters aren’t engaging in commerce with a larger society; it’s not like the monster is going to waltz into town and buy something. One possible explanation is that it likes shiny things, which is indicative of low intelligence. A better explanation is that a given monster happens to have valuables from killing someone and taking all their stuff, possibly indiscriminately, and having little or no idea that some of it is valuable. After all, why would it know this unless the monster was formerly part of a society and remembers this? Treasure attracts thieves, but then maybe the monster considers it a good way to lure people there so it can eat them.
Everyone needs to eat. The bigger our monster, the more food it requires. Large, four-legged animals like horses, deer, and bison are probably staple foods. Making it a vegetarian significantly reduces the threat to species, so you might want to avoid that, unless a salad eating monster is desired for comedic effect. If the monster just wants to eat, then survival is all it’s likely after, which causes an ironic problem if it feeds on the wrong thing…
For a storyteller, the biggest reason to have monsters eat intelligent species is for the horror it creates in others. For the monsters, they may have few other options. They also might not be sophisticated or moral enough to make a distinction. Feeding on the humanoid species, or livestock can rapidly cause conflict. Most monsters are remotely located, however, so wildlife is more likely to be a staple food. Humanoid species aren’t that appetizing, in reality, due to the ratio of bones to muscle/meat on us. This is why sharks spit out most people they attack; we aren’t a juicy seal, for example.
A monster that feels threatened is likely to attack others, especially those it believes to be encroaching on its territory. Monsters can be afraid, just as any apex predator can be. A monster could be smart enough to realize that attacking the species might bring greater numbers of them to destroy it, but it’s entirely likely that a monster doesn’t think that far ahead. Traditionally, monsters have a lair, which they presumably want to protect so they feel safe, but if our monster can fly or is otherwise quite mobile and a traveler, that greater freedom may give it less need of security. Then again, it might feel more vulnerable by not having a good place to hide. The idea of a monster who has recently taken up residence near a town is a good story premise.
Whether our monster resulted from an accident or not, it might want revenge on its creator. Does our monster know who created it? A monster upset with life itself might just want to kill from jealousy or hatred, but it’s often better in storytelling to have more interesting reasons than that. The “I’m a monster, therefore I kill” idea is stale. The monster might want revenge against the species that created it while leaving others alone. This can cause a perplexing mystery for characters. Imagine that elves caused the monster, who kills elves but leaves humans alone. The characters may not understand why at first until uncovering the backstory on this monster.