There's a ton of different types of Demons, ranging from Fire Demons, to (funnily enough) Light Demons, although there's a much larger variety of Demon than most people seem to think there are. Ranging from Yuki-Onna, or 'Snow Maiden', as they are sometimes called, to the tremendously rowdy and powerful Oni, there are many types of Demon that are flicked off as if they are simply old wives tales and superstition. I'll go over these here, and I'll try and explain in detail each type of Demon you may or may not encounter. Also to note, not all Demons are bloodthirsty killers, and most have integrated themselves into Human society quite nicely, not simply limited to Hell now that they're free to roam the Earth.
Elemental Demons!There are many elements in both this plane of existence, and the next. As such, there are many elemental Demons, Demons who have abilities linked with, or are able to embody, the elements, both natural and man made. These Demons are weak to a corresponding element, and so those who have become familiar with them have been smart enough to acquire weapons that have an elemental affinity that can repel, or even destroy their opponents with few hits. Here's the list, with a tidbit of information of each type as they're listed. Also to note, not all of these demons are capable of rational thought or emotion, so should you come across one, ask it if it knows what you are, and if it replies aggressively or doesn't reply at all, feel free to blast it into the next generation!
Fire Demons: These Demons are hot! Mostly in just the 'Ouch that burned me' sense, but sometimes in the other senses too. On a more serious note, these demons have the ability to manipulate, create, dissipate and rarely devour fire and it's sub-types. They mostly require no sustenance aside from being near to a living, burning flame for a few hours each month, or the can even hide in them and become a flame. They usually use the 'flame fusion' trick to surprise their prey, jumping out at the covered in blazing cinders, and rendering them to ashes. They are weak to water, water Demons and anything that could snuff out their flames.
Water Demons: Water demons are the polar opposite of Fire Demons, usually residing in tranquil, cool and usually peaceful locations. They are usually one of the smartest and humane forms of Demon, being able to calmly put together situations and speak as a human. Although most Demons are able to speak, Water Demons prefer to use their head instead of their fists, although if they're provoked enough, they won't hesitate to crush their foes with tsunami's and whirlpools. Their weakness is ice, or anything that can stop, or freeze, their water or them.
Ice Demons: Ice Demons live up to their name, being cold and hard as ice, and in some cases are actually formed out of it. They can freeze their opponents and can usually manipulate ice to their own whims and likes, and are a lot like the Water Demons personality wise, aside from their cold and aloof demeanor and the fact that they are easier to anger than Water Demons. They're usually found in colder climates, as opposed to the Fire demons living in hot climates and actual fire. They're weak to fire and heat, or anything that could melt them.
Electricity Demons: Electricity Demons are the most volatile of the Elemental Demons, being able to conduct, manipulate, generate, fuse with and travel along, electricity. They can drain their power from electrical items such as computers, and thus are extremely dangerous and should always be handled with caution, considering how much electricity is used to power things in modern times. They are both weak against, and powerful against, water. Water heightens their abilities, just like dropping a power cord into water as it's turned on, but if enough water is applied, they can usually be shortcircuited or depowered. Another weakness they have is earth, since their power is drawn to it, like lightning, and will diver any and all attacks, sometimes even absorbing them.
Wind Demons: Wind Demons are the calmest of the elemental demons, almost rivaling the Oni in their ability to take it easy and just not care about their opponents. They're also renowned for their laid-back personalities and their ability to power up almost anywhere and everywhere. As long as there's oxygen, they're fine. That said, they're able to effectively be the most powerful of the elemental Demons, since they can summon gale-force winds from out of, literal, thin air. They are weak to fire, since it consumes oxygen in order to burn, therefore erasing them from our realm.
Earth Demons: Earth Demons. The behemoths of the Elemental Demons, and usually the most physically capable. The most capable in, oh I dunno, maybe crushing you with their feet? Earth Demons are generally the largest, and the slowest, of the Elemental Demons. They draw upon the natural powers of the world around them, and the life that exists on Earth. They can manipulate the earth and it's aspects, ranging from flowers to stone, and can use them to form barriers and encase themselves in armour, but mostly they use this power to crush their foes, sometimes literally. Wind blows them away fairly easily, although some are resistant to this.
Darkness Demons: Darkness Demons are the most cunning, evil and deceptive Demons you'll ever meet. They hunt under the cloak of night, ambushing their prey with fear and shadows, before engaging in banter before chowing down. Usually, Darkness Demons are hideous creatures, but on occasion they are able to take more tempting forms, such as Children or attractive humans, though this is fairly rare. Darkness Demons grow weaker in the day, and they usually form a bubble of impenetrable darkness around themselves to stop the light from reaching in. Unfortunately, they have a habit of keeping this field up, even at night, which means that they are incapable of proper sight too far in front of them, and they are prone to flying, walking or running into things, because of this. They are weak against Light Demons.
Light Demons: Light Demons, the ones that are usually considered as 'Gods' and worshiped, although they do not accept such praise due to their modest personality and charms. They refuse to fight, instead always settling things with words and charms, due to the fact that they can't attack. The reason behind this is because all of their power goes into utilising barriers and shields, as opposed to the Dark Demons only being able to attack and not block. They counter the Darkness Demons, but can also be harmed by them, which is why they tend to be hermits and live alone, or surrounded by other Light Demons.
Magma Demons: Magma Demons are the brutes of the elementals, being nothing but dumb, and burning, muscle, they have no thought capabilities, and very little vocal skills to boot, meaning that they're always ignored or killed. The main reason that they're so dangerous is because they're made of magma, and constantly let off superheated steam, and the occasional burst of magma, which generally allows them to only exist inside volcanoes. They can control a magma, and the more skilled ones have a small amount of control over fire as well. Think of them as an upgraded Fire Demon, combined with an upgraded Earth Demon.
Crystal Demons: Crystallised Demons are made of pure crystal, being capable of both extremely powerful offensive attacks, and extremely durable defensive maneuvers, these guys are incredibly powerful and pretty darn intelligent to boot. They usually reside in one place, and can seem completely human in appearance aside from a small gem on their body somewhere, usually their forehead. They are usually the only Demons allowed to integrate into Human society, due to their ability to pass themselves off as Human. A contributing factor to this is the fact that they're usually the only kind who try to. Their Homes are usually made of nothing but crystals and shards, but if they live with humans, only their basement is like this. The rest of the house in normal. They don't age, but they can still be killed, although they've been rumored to live for millennia if undisturbed and in their natural crystal homes.
Zephyr Demons: Upgraded Wind and Electricity Demons, they can control Wind and Lightning, so they're fairly powerful by themselves, but paired with a Magma Demon, they can deal massive damage with their combined Fire-Wind attacks, and can devastate their opponents with their electrified bolts of energy. They're also nicknamed the 'Storm Demons', because of the fact that they usually only appear during stormy seasons or in stormy areas. They have the laid-back attitude of a Wind Demon, combined with the manic energy of an Electricity Demon, which can lead to some awkward situations.
Creation Demons: Hybrids of Light and Dark, these Demons can blind their foes with light, and impale them with spears of Darkness. They cloak in the shadows, and feast in the light. They usually appear as double sided, one being the beautiful holy vision of the Light Elementals, but when angered or provoked, they transform into the nightmarish visage of the Darkness Demons. They're usually calm and composed, but are prone to fits of anger and bloodlust. They are a very rarely seen Elemental, and therefore there isn't much information on them aside from the previously stated.
Rot Demons: Rot Demons are summoned by Jiang-Shi when the Jiang-Shi in turn are summoned, and they are undyingly loyal to their masters. Not that they have a choice, being essential zombies and all. they have nothing inside them except bile, which attracts other Rot Demons when it is 'bled'. They aren't technically an elemental, but they can be considered one.
Those are the currently recognised elemental Demons. Ones that have been sighted or killed, and had been reported to the Warriors of Divine Light. These all have a glaring weakness that can be exploited, aside from the Light and Darkness Demons, although they're usually never harmful to Humans in the first place.