Updated: Nov 24, 2020
When it comes to elementals, we discovered through our research that there is not much in the way of written research. It seems elementals are often mislabeled as something else such as demons or possibly fae.
Most elemental hauntings take place in isolated, mountainous, desert, or forest settings. It is rare for elementals to haunt within a city setting. The exception to this is if a person or group performs magical/magickal rituals, which directly invoke the elementals. Buildings used for religious purposes could possibly be elementally haunted. 
Earth Elementals: Gnomes
They often are found in deep forests and caves. They are also known as sprites, satyrs, pans, dryads, elves, and brownies. They can be helpful or harmful. 
Water Elementals: Undines
They are often found near ponds, rivers, marshes, waterfalls, oceans, and fountains. They are also known as water sprites and mermaids. They can also appear as human or small creatures. 
Fire Elementals: Salamanders
They have the power of fire and smoke, and often do not directly communicate with humans. 
Air Elementals: Sylphs
They are associated with clouds, gases, and winds. They are said to be a source of inspiration, but like all elementals, it could be helpful or harmful. 
Fifth Element: Consideration Elementals
These elementals are beings of ether or space. Some of the possible beings associated with these elementals include Jinn, grey aliens, and angels. 
Artificial Elemental: Tulpa
We have spoken often about manifestation theory, that the more belief, thought and energy you give an idea it is likely that you could manifest that idea and have it become an entity. When this practice becomes intentional is the same theory that we see in the creation of an artificial elemental or a Tulpa.
Many elemental spirits are often confused with human spirits, demonic spirits, angelic spirits, and fae.
Some of the ways we mix up elementals are:
Orbs of light could be fire elementals
Earth elementals are often confused with the fae
Air elementals often behave similarly to spirits in moving or throwing objects and have even been known to abduct people and cause episodes of missing time. They also have been known to leave fairy rings.
Water elementals can appear as human or even dark or demonic spirits.
Due to their dual nature of being helpful or harmful, they can manifest themselves as darker entities. Perhaps this is to protect themselves and their space.
Pagan has had a few elemental experiences of her own. You can listen to them in the episode.
Katie describes something "living in the catacombs" under the GRCC (Greater Rumford Community Center) S3E2 9min. She also describes the creature as crawling on all fours.
The more investigation crew of Haunt Me did at the GRCC the more they continued to see and more of the crawling creatures. Ultimately, they discovered that the crawling creatures were elementals from the river.
Sources and Links:
Haunt Me - GRCC Saga: https://www.youtube.com/playlist?list=PLKdnyTyfjR8HDgRjHp_O2XxKOkwrZu4_y