A well-utilized signature monster can drive a campaign for a long time.
The monster doesn’t necessarily need any exceptional abilities to be compelling.
For example, savage orcs move the adventures along in Middle Earth and skulking goblins jump start things in Golarian. There is something very basic in this approach, as the enduring popularity of zombie movies shows. Many players find appealing the idea of brightly shining heroes beating back hordes of brutes that are parodies of true men.
Not all monsters are outwardly monstrous. There is allure in exotic beauty and power, too. Good examples of this are the drow priestesses who scheme and plot in the Forgotten Realms or the gods and their agents who interfere in the affairs of mortals in Greek and Norse myths. Count among this archetype’s brethren inscrutable alien aberrations, arachnids and insects, and hosts of demonic and supernatural foes.
And of course, we have the dragon, and all its cold-blooded kin, such as dinosaurs and lizards. Mammals are repulsed and captivated by the reptilian and serpentine, and fire-breathing dragons are the apex of this expression. St. George, Chinese mythos and Dragonlance have all been expressions of this magnificence. And if you prefer your dragonkin more manageable, feel free to kick around some kobolds. (Really, I insist.)
Of course, the greatest monster is us, the human being. Depraved and duplicitous, short-sighted and greedy, some GMs prefer not to disguise evil, but hold up a mirror to it. But for the purposes of this article, we’ll set aside Homo sapiens sapiens.
Now that we’ve got these archetypes properly categorized, let’s crack open a monster book or two for some different monster descriptions that might be good campaign fodder.
Fomorians are D&D Fourth Edition’s re-imagined hill giants, incorporating elements of Norse and Tolkienesque trolls by making them more industrious and intelligent. These hideous hulks emerge from their impenetrable mountain caves and attack remote settlements for slaves, breeding stock and to fill their cook pots. Their motives are standard for the brutish humanoid, except the fomorians have origins tied to fey realms, therefore, access to magic. In addition to being a substantial threat themselves, they are a good linking monster: fomorians can be masters of lesser monsters who direct their destruction and they can be servants and do the bidding of more powerful creatures.
Alien and Exotic
One of the things Paizo has done well with Pathfinder is mine real-world mythology and put a spin on it. Divs, the Slavic house spirits, are such an example. In Pathfinder, these become a host of befouled genie spirits who give their allegiance to the bestial fiend Ahriman, working to undermine civilization and torment humanity. There are dorus, the dark whisperers and corruptors of conscience; aghash, desert hags that are the embodiment of the evil eye; pairaka, temptresses who undermine the good; ghawwas, demons of the sea; shiras, bestial stalkers; sepids, warlords of slaughter and akvans, princes of destruction. Each div presents a different kind of challenge, ensuring a host of foes over a long campaign.
Though designed for player characters, the dragon-inspired races of dracha and mojh of Monte Cook’s Arcana Evolved present an interesting challenge as adversaries. Each represents a component of the great dragons, dracha their physical might and power of flight, mojh their intellect and magic. They can serve as forerunners of a dragon invasion or servants of a threat that has not yet been revealed. Transformation from one form to another, including gender, is a theme the Arcana Evolved setting emphasizes, meaning evolved and transitional forms of dracha and mojh can be used to add variety to combat challenges. It also means psychological and societal issues related to transformation can be explored within a campaign.