Elemental

Elemental refers to both a type of creature, and to the specific incarnations of the four classical elements: air, earth, fire, and water.

General characteristics
Elementals are manifestations of an element. The Monster Manual, 5th Edition, which may not be canon for Critical Role, notes that on their home planes, elementals are formless spirits unless focused by magic, and they are analogous to animals on the Material Plane in their motivations and sentience. All are immune to poison, resistant to physical damage from nonmagical sources; and cannot be exhausted, paralyzed, petrified, or knocked unconscious.

Air

 * Djinni: The genies of elemental air.
 * Invisible stalker
 * Air elemental: Air elementals have a tornado or whirlwind-like appearance, with a barely-perceptible face.
 * Lightning spirit
 * Maelstrom: An enhanced air elemental with a much higher armor class, hit points pool, slam reach, attack modifier, damage capabilities, and ability power. Maelstrom, who inhabit the Glintshore, gather the broken glass and sand of island into their vortex, dealing piercing damage with their Whirlwind ability instead of bludgeoning.
 * Storm spirit

Earth

 * Earth elemental titans
 * Dao: The genies of elemental earth.
 * Earth elemental: Earth elementals have a vaguely humanoid shape, but are made of dirt and stone.

Fire

 * Phoenix
 * Efreeti: The genies of elemental fire.
 * Cinderslag elemental
 * Fire elemental: Fire elementals set their surroundings alight, and can be stopped with water.
 * Fire gila
 * Salamander
 * Azer
 * Fire snake
 * Magmin
 * Wildfire spirit: Elemental familiars summoned by Circle of Wildfire druids.
 * Thordak's spawn were primal elemental dragons.

Water

 * "Elemental leviathan"
 * Marid: The genies of elemental water.
 * Water elemental: Water elementals are shaped like tidal waves and can engulf their foes.

Mixed elements

 * Cold snap spirit
 * Dust Titan
 * Frost salamander
 * Dust mephit
 * Ice mephit
 * Magma mephit
 * Smoke mephit
 * Steam mephit

Related race
One of the origins of genasi is as descendants of the genies of various elements: air genasi descended from djinn, earth genasi from dao, fire genasi from the efreet, and water genasi from marids.

Pre-stream
During the Founding, the Primordials' slaughter of mortals set off the schism between the Betrayer Gods, who wanted to join with the Primordials and allow chaos to reclaim the world, and the Prime Deities, who wanted to subdue the Primordials to save their mortal creations. The slaughter also drew demons from the Abyss and celestials from a far-away realm. Eventually, the Primordials were defeated and locked away in their own elemental planes. But the battles left lasting marks on the world. A Primordial earth titan, in its final battle, was slammed into the ground violently enough to create the Zenwick Mountains. And at the end of the Founding, primeval elves felled the Molten Titan, giving birth to the Daggerbay Mountains.

In the early Age of Arcanum, the dwarven Thomara clan dug into the fallen earth titan in the Zenwick Mountains to exploit a precious metal vein cluster and built a vault city there. The society eventually collapsed into madness and cannibalism.

Around a century or two before the Divergence, during a celestial solstice, elemental rifts burst open across Exandria, causing fires, earthquakes, and an outpouring of elemental monsters whom the people of the world struggled to combat. The Ashari, up to then a nomadic people, divided into four tribes to seal and watch over the largest rifts to the Elemental Planes of Fire (Pyrah Tribe), Water (Vesrah Tribe), Air (Zephrah Tribe), and Earth (Terrah Tribe), ensuring that nothing dangerous can pass through to the Material Plane.

Several centuries later, only two years after the Scattered War, another celestial solstice paved the way for another elemental invasion. Errevon the Rimelord opened a rift from the Frostfell to what would later be called the Frostweald, beginning the Icelost Years. With an army of frost giants and sentient blizzards, Errevon conquered most of the continent of Tal'Dorei in a few years. In time, the Council of Tal'Dorei convinced Syngorn and Kraghammer to join in an alliance against Errevon, and together their forces battled Errevon back through the rift, which the Ashari druids sealed shut. The victory was later celebrated annually as the Winter's Crest festival.

Campaign 1: Vox Machina
As a Circle of the Moon druid, Keyleth could wildshape into elemental form, and often did so in combat. Vox Machina encountered elemental foes several times, notably fire elementals at the portal to the Elemental Plane of Fire in Pyrah, and water elementals as they approached Vesrah. Keyleth's Spire of Conflux also had the capacity to conjure elementals.

Thordak, who had been bound to the Elemental Plane of Fire with an elemental heart crystal, was transformed by the experience. Thordak asexually spawned several primordial dragons, found in his his crater in Emon.

Campaign 2: The Mighty Nein
The Mighty Nein also faced elementals in the fight in which they freed Xundi, and fought them several times in Eiselcross. Beau had an elemental gem looted from the Sour Nest which permitted her to summon a fire elemental, which she did against Thelashas.

Notable elementals

 * The Primordials
 * The Molten Titan whose death created the Daggerbay Mountains
 * The earth titan whose death created the Zenwick Mountains, in whose body Thomara was built, and which Vecna animated to attack Vasselheim.
 * The Dust Titan encountered in Pandemonium by Vox Machina in
 * Errevon the Rimelord, who invaded the new realm of Tal'Dorei, bringing about the Icelost Years
 * Marrake al-Sidan al-Hariq ben Lazen, Grand Sultan of the City of Brass
 * Khedive Xundi, a marid whose home is the Silver Silt Palace in the Elemental Plane of Water but who was enslaved for the benefit of Nicodranas
 * Little Mister, a wildfire spirit that takes the form of a monkey, who bonded to the faun Fearne Calloway