Having chatting with Karma about the story, I've offered to run a band of human hunters as NPCs if/when we can get this off the ground. (I might also run a merman, but that is up in the air... or more accurately, the water) This way whomever does end up GMing has one less set of "Bad guys" to worry about running. I do not have time to GM myself, as my 1x1 partners do take priority.
It's for a lot of reasons, including those. They seem impossibly numerous and spend most days "increasing their ranks." They are technologically advanced (for the setting, they don't have computers or anything), they have a strong innate resistance to magic themselves, and probably most importantly, the vast majority of halmons don't have any magic that they can use for fighting. A cowgirl doesn't have much advantage over a human except hardiness and horns, for example. Some do have powers, of course, but they are much less common. Much of the magic in the world that could be used against humans is contained in elven technology which is very hard to find.
The humans as I see them might have one or two firearms per hunting group, but they would be of matchlock or wheel-lock variety. This means that they will be limited range, heavy, inaccurate, noisy, smokey, and (most of all) expensive. Powder would not just be wasted on any old monster that comes along! The humans would be hunting with bows, spears, swords, axes, fire, snares, traps, and their most deadly of weapons, their wits. In keeping with the setting as described, being shot is bad but being hacked apart is horrific.
As mentioned, the humans have a "strong innate resistance to magic." Which I take to mean that a Siren or Succubus or Incubus (for example) might charm one or two hunters, but not the whole band at once. A Demon calling up dark forces to obliterate an opponent or a Dragon breathing magical fire might only injure or hinder the target. I would not take it to mean that humans are totally immune to magic, nor are they impervious to things like claws, teeth, horns, talons, or other sharp body parts that could rend them apart in seconds. Nor would they be immune to things like being stuck in an Arachne's webbing or being drown by a Mermaid. Ultimately, some sort of group consensus would have to be had on this, though.
As gory as the players want it to be! And of course nothing will happen to your characters that you don't want.
As Karma has pointed out, consent is all. While the setting is one of horror and conflict for the characters, it's supposed to be fun for us as writers.
That being said, keep in mind that if you decide you want your character to be hunted, then that is exactly what will happen along with all the consequences of being caught; being enslaved, abused, tortured, raped (if the monster is "human" enough), killed, gutted, and eaten are all possibilities. Some humans will be cruel, some will be merely efficient, but either way the vast majority of them are going to be of the mindset that the halmon are nothing but animals, resources to be harvested and used.
Now before this all sounds too one-sided, please keep in mind that turn about is fair play and that this street goes both ways. A hunter who is unwary enough or unlucky enough to be lured into a trap set by monsters or be ambushed gets what he or she deserves. I have no issues with my characters dying or suffering similar fates to the ones described above so long as it serves the story. I will add that not all human are completely unsympathetic to the destruction they've caused (only about 5% or so, but it's something, right?), so it's entirely possible that killing a lone human might mean killing a potential ally. Then again? It might also make for one hell of a poignant moment!
Here's hoping we find a GM or a couple of co-Gms soon, and we'll see what happens!