The term "monster" does not refer to a singular race. Rather, "monster" is a classification of race, like "Non-Magical" or "Magical".
Monsters are special hybrids created by the Goddess Umumtu for the purpose of both understanding how to fuse Magical and Non-Magical creatures together, but also to create servants who can survive in the Living Realm. These creatures are all corruptions of other creatures that already existed in the Living Realm; since Umumtu does not have the ability to grant Living Force to her creations, she has to take a creature with Living Force and corrupt it to create a new race.
Because monsters are —from a very practical perspective— disposable creations, their existences tend to be very tragic ones. While some are able to live good lives in harmony with the rest of the Living Realm, they wouldn't be called 'monsters' if that were common.
Monsters come in two forms, sentient and non-sentient. As the name implies, sentient monsters are self-aware with the full range of emotions, rational thinking and thoughts as any other sentient race. In fact, the founding monster of each race started life as a Non-magical creature who was corrupted with magic (and possibly combined with a non-sentient creature).
Note: Due to the nature of Monsters, non-sentient monsters tend to be agressive, dangerous beasts. Even by other monsters, they are to be avoided as they are not above feeding on another monster's magic to survive.
Monsters, while varied in appearance and abilities, are the most uniform of all racial classifications. Because they are all created by Umumtu with the same goal in mind, they all have the same basic gifts granted by her
Umumtu is known as a lover of the female form, and her creations have a tendency to reflect that. She prefers smooth and curved forms to harsh, jagged, or blocky ones. She has very little use for men, in general, often being impatient with them, or dismissing their opinions outright. As such, many monsters are either mono-sexed (all female), or are more often biologically female than male. This varies by race (though some races are far enough from humanoid that sexing them is often difficult).
Because of this lean towards an abundance of females, most monster societies are matriarchal. This has lead other races to mistakenly believe that monsters are all female, even when that's not always the case. Most people will default to 'she' for a monster of unknown gender.
Because of their creator's bias, most monsters feel a strong pull towards feminity, both in sexuality and in gender-identity. However, these are broad strokes and sentient monsters are as varied as non-monster races. There are gender-fluid or non-binary monsters. In fact, some monster races have the ability to change their forms which leads to a sort of inherent downplaying of gender, as biological sex becomes something more akin to fasion than a fact. After all, among all shape-shifting races there is no such thing as 'biological' sex; they can be whatever sex they wish, regardless of what gender (if any) they identify with.
All monsters in the Living Realm survive by draining the Living Force from other native creatures. This drain can be passive (merely standing near non-monsters), or it can be active (i.e. drinking blood, consuming flesh, copulation, etc). Monsters must have either a source of Magical Force or Living Force. If they drain Living Force they will produce Magical Force.
There are several sources of Living Force. Living creatures generate it, and places filled with abundant plant and animal life are often pools of such Living Force. Simply by spending time in these locations, a monster may be able to gain enough Living Force to survive.
There are, however, more potent sources. The blood of living creatures is one of the most potent forms, especially that of sentient creatures. (Human blood is the most potent of all.) Similiarly, other bodily fluids (especially those of a sexual nature) are concentrated sources of Living Force. Intense emotions are also a good source, however positive emotions are a better source than negative ones, though both can sustain most monsters well enough.
By gathering together in communities, monsters create areas of Magical Force that help sustain their population. (Especially if they convince non-monsters to live with them, either through friendship, marriage or coersion.) However, if their population grows too large, it will draw attention, as their need to feed will start leading some members to attack non-monsters. When this happens, most monster communities split, with the agressor leading one group to found a new community.
Even sentient monsters are monsters, with a bestial nature. If they are not well fed, even the sweetest, most even tempered monster can, if starved, grow ravenous: seeking to gorge themselves on as much Living Force as they can aquire. When this madness takes them, they lose all rationality and give in to their basest desires, become worse than the non-sentient monsters. They will gorge themselves until they are bursting with Magical Force, at which point the madness will cease and they are left to witness the consiquences of their hunger.
It is because of this danger that most monsters live isolated from non-monsters. This self-imposed exile is less about protecting others, and more about avoiding the overwhelming guilt and self-hatred that often comes from such an episode. Monster communities work hard to keep each other well-fed so such incidents do not happen.
Individual monsters have been known to become ferral, seperated from the aid of others and unable to saitiate their hunger. If they attack too often they will start to gain a taste for it, indulging in the euphoria and complete release of their own will to the hunger. Such monsters are amoral beings of pure carnage, often hunted down and killed by non-monsters. (Sometimes they are even hunted by their own kind, out of a desire to prevent the predjudice, fear and hated often generated by such acts.)
For reasons that are not even entirely clear to Umumtu herself, monsters in the Living Realm are far more physically and magically strong than when in the Magical Realm. They approach the strength of Celestials or Infernals. The older the monster, and the deeper their store of Magical Force, the more overall powerful they are.
Even a weak, starving monster is physically stronger than most Non-magical races, save for some Orcs and Dwarves. This is what makes monsters so ill-trusted; a single monster can wreak havok that is hard to stop without several strong Non-magical creatures.
Because the method for creating monsters is difficult and involves the abduction of a non-monster, Umumtu gave monsters the ability to reproduce with almost any creature that contains enough Living Force. Monsters reproduce very quickly, with some races having as little as a three week gestation cycle. The offspring is always a monster of the same race as the parent.
Note: Sentient male monsters must find a sentient female to reproduce with, and she carries the child to term. These pregnancies are often difficult, resulting in miscairrages or still-births. Female monsters are able to reproduce with any creatures with enough Living Force, regardless of sentience, and as they carry the monster-children to term themselves, the pregnancies are no where near as complicated.
Note II: Non-sentient monsters can reproduce simply by consuming enough Living Force. They tend to have the quickest gestation cycles, meaning a monster population can explode almost over night.
Monsters reproduce quickly because they also die quickly. They are frequently hunted by non-monsters (both to reduce attacks, and for the properties of their magical bodies as components for potions or spells or other magical uses.) While the sentient monsters tend to live longer by forming communities, it's not uncommon to hear about entire monster communities being attacked or killed.
There also seems to be some other forces at play here; sometimes monster communities are found with all members having been killed, but no signs of what killed them. It is believed that this is the workd of Veza or her agents; no normal non-monsters would be strong enough to take out entire communities at a time.
While several races (both monster and non-monster) frown on it, it is not uncommon for monsters to seek out non-monster partners, either for casual liasons or as romantic partners. These partners provide not just the normal companionship such an arrangement normally entails, but also grants the monster a source of Living Force, allowing them to live comfortably with a lessened fear of losing themselves to the hunger.
It should be noted, however, that the bias against such arrangements, while only shared by a minority, is incredibly strong. They see monsters as vile, unclean things, believing the partners to be hapless victims (at best) helping the monster secure their reproduction.
Even normal non-monsters are often hesitant; not only is there the inherent fear of being attacked or killed by the monster or their kin, there's the fact that all their children will be monsters themselves. Monster partners often feel like outsiders in the monster community, never fully able to understand their sposes or children.
Note: The only reason to call out monster marraige is because it's so controversial. Monsters, by their nature, are often antithetical to the existence of their non-monster partners, making the pairings often frought with tragedy.
Since monsters are Magical in nature, they all have magical abilities, which are unique to each race. However, they all live much longer than most Non-magical races. It is believed that a well-fed monster can live effectively forever, as if they were living in the Magical Realm.
While not all individual monsters have easy access to the Magical Realm, they are —due to their nature— able to find location of Magic, or sense portals to the Magical Realm. Most of the sentient races will teach their members how to open a portal, though not every monster learns to do this. They all can, however, sense one that has been opened and sometimes intuitively reopen a recently closed one. While this is intended to make it easier for them to report any rumors of Veza, it can also be used by a desperate, starving monster as a way to return home.
Note: Monsters can also instantly recognize a Magical creature, even if they're disguised or using a shape-shifting ability. They can simple sense the magic coming off of them.
See monster creation on the mythology page.
Since monsters started arriving in the Living Realm, thier history has been one of persecution, hatred, and devotion to their singular mission. The monsters in the Living Realm (generally) are there by choice. They know their purpose and have dedicated their lives to it.
Over time, however, some monsters have simply grown to love their life in the Living Realm. There is the constant risk that they will be hunted down by whatever mysterious forces seem to hunt them, or even just nearby non-monsters banding together out of fear, but they accept that risk. They love their lives and would rather stay here than return to the Magical Realm.
It has been long enough since the creation of most monster races that many question the futility of searching for news of Veza. Almost all monsters know it's their 'duty', but increasingly monsters are ignoring their calling. They simply wish to exist.
Because most can return to the Magical Realm, those who find the search futile often end up returning home. Still, Umumtu has not given up the search, and she is not above visiting a newly returned monster to 'encourage' them to return to the search. A visit from the Goddess can be a powerful thing.
Monsters are the only creatures to live in both the Living Realm and the Magical Realm. They can, with only mild difficulty, move between the two realms. Many monster races return to the Magical Realm either to raise children or to find mates as part of their culture. Others, conversely, live primarily in the Magical Realm, only venturing into the Living Realm to find a mate and reproduce.
When in the Magical Realm, monsters are no different from other Magical creatures, only weaker. The hunger they feel in the Living Realm is gone, and many find spending time 'at home' in the Magical Realm helps cleanse and center themselves.
Because of this, some monster races choose to raise their children in the Magical Realm, training them with brief forays into the Living Realm to curb their hunger, and making sure they are as well prepared as possible for life in the Living Realm.