"If you've not averted your eyes, you'll notice that the ground is full of monsters. They are impure creatures, yet no one tries to remove them; no one tries to bring peace. Why? Because humans are weak, cowardly creatures."
- --Vinsfeld Rhadamanthus
Filgaia is a dangerous world. Year by year, the desolate spaces grow, and the things within them get bolder and deadlier. Some of them are Filgaia's original inhabitants--creatures trying desperately to survive on their dying homeworld. Others are much stranger, raising the question of whether they're natural life or the creations of some long-dead civilization. The line between the two is blurry, and few Drifters have time to care about it when there's a slavering monstrosity trying to claw out their throat.
On the surface, Lunar is a calm and idyllic in comparison, but it too has its monsters. Althena's blessing brought life to desolation, but not all of that life is friendly to Lunar's sapient inhabitants. On top of that, creatures with strange and sinister powers arise with alarming regularity, requiring Lunar's defenders to keep watch for signs of corruption. Anything can fall prey to it, and this fact has influenced Lunar's inhabitants more than many would care to admit.
As can be expected, most of Filgaia's surviving wildlife is well-adapted to its harsh, unforgiving land. In most regions, the surviving plant life consists largely of scrubby grasses, and analogues of small trees, cacti, and tumbleweed-bearing plants. Filgaia's forested regions have to cope with decreasing rainfall, and frequent fires--in another century, they might not be around. As can be expected, this puts a great deal of strain on the planet's food web, and its surviving animal life includes many organisms that are adept at exploiting new food sources. Unfortunately, many of these organisms view humans as protein on two legs.
Filgaia is littered with the debris of advanced civilizations, some of which were advanced enough to create artificial life--semi-autonomous ARMs that could operate with or without someone to guide them. While Filgaia's wildlife tends to use ruins as lairs, most Drifters know that any construct encountered in a ruin was likely left there for a reason. While many have succumbed to ages of neglect, others remain perfectly functional. Wise Drifters know better than to assume a construct is out of action, no matter how dilapidated it looks. A seemingly-broken machine can easily become a mortal threat if someone opens the wrong door or investigates the wrong terminal.
Constructs vary in nature, ranging from clay or stone effigies animated by Symbology or Crest Magic to high-tech machines with complex weapons and internal power supplies. The most esoteric of the lot are traditionally attributed to the long-vanished Elw. A handful of these constructs were recently unearthed by Adlehyde -- dubbed "Golems," they're nothing less than colossal siege machines, constructed to fight some ancient enemy. Though all are at least marginally intelligent, they possess potent control mechanisms, allowing an operator to restrict or direct that Golem's actions.
The Metal Demons didn't wage war on Filgaia alone -- they brought equally-bizarre organisms to serve as their shock troops. These creatures, known to many as Metal Beasts, were the vanguard of the invasion, and while they had many physical traits in common with Metal Demons, they lacked the Demons' intelligence. Most Metal Beasts served as scouts, reavers, and general cannon fodder, and the Metal Demons saw nothing wrong with sending them off to die in droves. After the war, the Metal Beasts vanished alongside their masters, and they remain little more than a footnote in a history already filled with legends and uncertainties. Every now and then, a Drifter returns from the wastes with tales of strange creatures with metal flesh, but none have been able to offer solid proof.
Few monsters are as universally feared as the Wels. These creatures vary widely in form, but all share two characteristics: disturbingly malleable bodies and an insatiable hunger for human flesh. Though at times hindered by their own misshapen bodies, the Wels have an innate sense for prey, and they exhibit single-minded determination when trying to get at it. A whole horde of Wels can easily overwhelm a small town, and more than one settlement has met this fate. To many in Aquvy, the Wels are known as Reapers, and they've earned the name many times over.
Alarmingly, the Wels can turn numbers to their advantage in other ways. If there's no prey to be found, a group of Wels will inevitably resort to cannibalism, devouring each other until only a single, massive Wel remains. These Gear-sized monstrosities are mortal threats to all but the most well-defended cities -- and priority targets for the Ethos.
Many of Lunar's monsters are organic in nature, unlike the mixture of organic and construct monsters found on Filgaia. Filgaia's most fearsome foes are not to be found on Lunar. Wels, Constructs, and Metal Beasts are nowhere to be found. Instead, aggressive wildlife is the most common. Of course, there are other threats unique to Lunar.
Hellions are beings that have been twisted into a monstrous form by Malevolence. Some of them are not only powerful, but intelligent as well, and capable of disguising their true form. Almost all of them were once humans or Seraphim, and are covered in the races file. The vast majority of Hellions are altered beasts or intelligent creatures turned against their will into mindless monsters. To the human eye, they may appear only to be a larger, more dangerous animal or a creature such as a lizardman. They can possess surprising strength, however, and sometimes utilize magical effects well beyond what natural creatures can do. Regardless of what they look like, most people don't perceive or remember weaker Hellions as what they really are. Unlike their stronger brethren, they can't voluntarily show their true nature. Someone who survives a Hellion attack might remember a pack of wolves, or some other type of monster--but not a Hellion.
Those turned into Hellions can only be purified through very rare magics granted by the Seraphim (or, perhaps, another divine power). They can be killed, however, and this is often considered a mercy.
Fiends are creatures born of pyreflies, when a person or beast dies without a Summoner to do a Sending. Fiends form naturally and frequently in Spira. They are unable to form outside of Spira, though a Fiend could hypothetically be transferred there. Fiends assume many shapes and sizes, but all are fierce and hostile to those they encounter. Bevelle’s Warrior Monks and the Crusaders are charged with keeping Fiends away from the villages, cities, and highroads of Spira; only the foolhardy (or Summoners and their Guardians) tend to venture off the beaten track.