All elementals have access to elementium and enchanted elementium. Each have their own unique material as well.
None of the elementals use armor, shields, or wear clothes, and all of them are tier 4 invaders.
Most of the civilized elementals dont leave behind corpses - the only exceptions are earth elementals, flamefiends, and the "leader" castes. Otherwise, most elementals drop elementium bracelets on death (unless noted that its a different piece of equipment instead).
Earth Elementals - found in fortresses in the mountains and deserts. Their unique material is Obsidium, a lightweight, sharp but fragile material.
Castes:
Earth Elemental - standard caste, they are twice as large as humans. No special abilities.
Earth Drudge - a "lower" caste, they are only slightly bigger than dwarves, and are excluded from most noble positions, serving only as laborers. As they are properly humanoid, they have kicking attacks.
Earth Warrior - a warrior caste, they are more than five times larger than humans. They can bite, on top of kicking, but are otherwise purely physical attackers.
Earth Princess - a female noble caste, they are the same size as Earth Warriors. They have four arms, and three faces. They can throw bolts of stone, and also kick up either directed or undirected waves of dust.
Stonemother - leaders of the earth elementals, they are the largest and most powerful of them as well. They can throw stone bolts at up to 4 targets, and aside from kicking up directed/undirected waves of dust, they can induce debilitations with Reverberating Pulses.
Earth elementals aren't innately hostile (unless you play as ogres), but due to their rather strange values may still end fighting your civ in worldgen.
For weapons, earth elementals use mostly axes and spears, but also some larger sword variants.
Water Elementals - found in towns in the wetlands, taigas and forests. Their unique material is Hydrocite, which is a dense and protective material.
Castes:
Water Elemental - standard caste, only slightly larger than humans. They lack fingers, but their "jab" attacks still inflict edged damage. They can shoot Water Bolts - pressurized water that does blunt damage.
Water Prince/Princess - noble caste, twice as large as standard water elementals. Due to their more "defined" shape, they have regular scratching attacks as well as biting attacks. Aside from Water Bolts, they can spray scalding water at their foes.
Tidehunter - water elemental leaders. Their torsos are scaly and made mostly of flesh materials. They can shoot water bolts at up to 4 targets, can release waves of scalding water either in a directed stream or undirected wave, and can also cast Frost Shock.
Water elementals aren't hostile by default, but as with earth elementals their values are rather strange and may result in worldgen fights.
They utilize a few types of maces, and aside from that use spears, tridents and various forms of straight swords.
Fire Elementals - found in fortresses in the deserts, grasslands and shrublands. Their unique metal is Incedicite, which is above-average compared to other elemental metals, not excelling in one area or the other.
Castes:
Fire Elemental - standard caste, slightly bigger than humans. Their only special ability is to fire bolts of magma.
Firelord - one of the "noble" castes. Their chests and shoulders are armored, and they wear a metal crown. They are more than twice as large as standard fire elementals. Aside from shooting magma bolts, they can cast Soul Burn, which causes severe pain, and reduces willpower, focus and strength. Additionally, their scratching attacks cause incinerating wounds, which induce blisters and make the bleeding more severe. Instead of dropping bracelets on death, they leave behind elementium Firelord crowns, which can offer some amount of protection.
Flamefiend - secondary "noble" caste, slightly larger than the Firelord. They are made of both elemental energy and stone, and they have armor on the lower body, head, neck, lower arms, lower legs, hands and feet. They are capable of flight as well. In terms of abilities, they can hurl magma bolts and release directed streams of flames.
Avatar of Flame - fire elemental leaders. They have armor on their chests and upper arms, and also wear bracelets. They can release either directed or undirected waves of flame, cast Soul Burn, and cast Dreadflame, which causes severe bleeding, pain and blistering, while also reducing endurance. Their scratching attacks cause the same incineration affliction as one from the Firelord.
Fire elementals have a varied set of weapons - hammers, pikes, spears, swords, some maces and axes. They send out snatchers and are innately hostile.
Air Elementals - found in towns in the mountains, savannas, shrublands and grasslands. Their unique material is Aerocite, a lightweight, protective but also sharp metal.
Castes:
Air Elemental - standard air elementals, their only ability is to shoot bolts of lightning for blunt damage.
Air Prince/Princess - air elemental "nobles". They only have one eye, and are five times larger than standard air elementals - their shoulders and heads are also armored. Aside from firing lightning bolts, they can also cast Paralyzing Shock, and can also release an undirected wave of cutting wind. On death, they drop elementium helms.
Windlord - air elemental leaders. Their shoulders are armored, and their lower arms and heads are wrapped in cloth. They can fire lightning bolts at up to 3 targets, cast Cyclone, Paralyzing Shock, and also released both directed and undirected waves of cutting wind.
Air elementals use mostly spears and curved swords - they are also the only elementals that use ranged weapons - throwing daggers and javelins.
They send out snatchers, and so are always hostile.
Twilight Cultists - cultists of various races that worship the Old Gods and seek to bring about the end of the world. They can use all of the elemental metals, along with Enchanted Elementium.
All of their castes are fearless.
Castes:
Twilight Cultists - mortal human cultists that still have no magical powers. Aside from being fearless, they aren't different from normal humans.
Chosen Cultist - two-headed ogre cultists. They are support casters of the cultists. They can buff their allies with Bloodlust and Shadow Shield, which doubles toughness and makes them feel no pain. They can also cast Curse of the Elements, which can make some of the elemental attacks of their Ascendant allies more devastating. They are otherwise no different from regular two-headed ogres.
Twilight Zealot - orcish cultists. They are melee fighters, and utilize self-buffs - they can use Shadow-walk, which temporarily raises their speed to 300% of its normal, and Twilight Infusion, with doubles their strength but reduces their toughness to 60% of its normal. Otherwise, they are the same as normal orcs.
Fire Ascendant - fire elemental ascendants. They can throw magma bolts and cast Soul Burn, and their skin is made of volcanic rock. All ascendants have the same body build and size (more than three times as large as humans)
Earth Ascendant - earth elemental ascendants. They can release Reverberating Pulses and throw bolts of stone. Their skin is made of stone.
Water Ascendant - water elemental ascendants.
They can spray scalding water and cast Frost Shock. Their skin is made out of gemstone.
Air Ascendant - air elemental ascendants. They can release an undirected wave of cutting wind and cast Cyclone.
Elementium Monstrosity - the most rare caste of the cultists, they are also the largest, but are forbidden from all noble positions. They are genderless and combine the four elements - they can cast Soul Burn, throw bolts of stone, release a directed stream of cutting wind, or an undirected wave of scalding water. Their skin is made of metal.
Twilight Harbinger - the second most rare caste, and also the leaders of the cult. They are highly mutated two-headed ogres, with eyes in places where they don't belong and rocky growths on their fingers, toes and backs.
They can hurl shadow bolts at up to 3 targets, cast Corruption, Oblivion, and Shadowflame, which causes strong pain, blistering and bleeding, and also cuts endurance to 60%. Since they count as eldritch creatures, they can be afflicted by spells like Turn Evil.
They have a very varied set of weaponry. However, for protection they only have shields and masks - they don't use any sort of practical armor, only regular clothing.
They send out snatchers and are always hostile.