Humans are far from the only intelligent species on Earth! They just like to think that they are.
This list is by no means exhaustive or comprehensive! It is only a chronicle of species that have already been revealed in Moe Lord or are planned for the near future.
Humans are the current dominant species on Earth. In the past they were known for their skill with magic, but now only a tiny fraction of them even know it exists thanks to the effects of "The Outcasting". Their dominance over the Earth is maintained through advanced technology.
Despite the high number of countries and constant warfare across the Earth, Humans are probably the sapient species with the greatest ability to form large, complex societies. Humans are also well known for their art, domestication of many species, and the invention of the snuggie.
Fairies are flying, magical beings. Almost all fairies are small, but those of royal blood grow to about 2.5 feet tall, or however much that is in centimeters. Most fairies know spells that are helpful or defensive in nature, but can produce powerful attacks when working together. Once the allies of humans, they have now allied themselves with demons and the Demon Lord.
Goblins have no ability to perform magic by themselves. To compensate, they have become masters at alchemy and the smithing of magical instruments. Goblins are the true original creators of many inventions now considered made by humans, such as firearms, woodblock printing, and deep fried butter. Once the allies of humans, they have now allied themselves with demons and the Demon Lord.
Infernals live between the Earth's crust and its mantle. They are powerful creatures made of fire and lava and ash, semi-intelligent and posessing of powerful magic. For an Infernal, physical strength and powerful magic are directly related, and no warrior can posess one without the other. Hybrids of this species with others are extremely rare but not unheard of, and usually require the assistance of magic to produce.
Elves are fucking dead. Deal with it.
Beastmen are animal/humanoid hybrids, such as pigmen or wolfmen or mantismen. It's best not to think about where they come from. Although powerful, they are very few in number.
Tanuki are shapeshifting raccoon-dog creatures that dwell in Japan. I think they have huge nutsacks or something.
Kappas are turtle-like humanoids with bowls of water on their head. If this water spills out or dries out, they become frozen in place like a statue. They're only mildly intelligent, and mostly known for sumo wrestling.
DemonsEditImps are considered the lowest and weakest of all demons, ranging in size from the size of a human thumb to around 2 and a half feet tall, or however much that is in Yen. Like fairies, it's rare to see Imps with abilities tailored to direct combat.
Succubi and Incubi, collectively known as Sirens, are shapeshifting demons evolved to prey on humans by seducing them and stealing their souls. During the Great Demon War they were used as spies or agents due to their ability to take on human form at will, but they've integrated so well into modern human society that most that live on Earth have lost interest in the demon world altogether.
Fiends are a "miscellaneous" class of demons, a title assigned to beings unique or strange enough that they don't fall neatly into other categories. Lesser, regular, and greater fiend are all classes commonly found for individuals in the demon population.
Archdemons are mighty, proud, gross monsters similar to the demons in the Ars Goetia, or the Greek monster Typhon. Their most peculiar feature is the large number of limbs they have, coming from a wide range of animals and mystical creatures, like a weird mish-mash of living things. Most of them opposed Mortem during his rise to power, which got nearly all of them killed and greatly reduced their numbers. Probably about ten are still around.
Devils are possessor demons of a particularly nasty nature. Victims of Devils are characterized by glowing eyes and weird shit coming out of their mouths. They've been hunted to near-extinction by Magical Girls.
Djinn are mysterious beings from origins unknown that reside within certain objects scattered throughout Earth and the Netherworld. If a mortal finds these objects the Djinn is required by some sort of code to grant the moral a set amount of wishes, usually three. Freed Djinn are weaker than their bound counterparts as their homes granted them additional power, but they can still be quite threatening. Freed Djinn have vague and complex limitations to their powers, and they prefer to work behind someone else rather than act directly.