Atmospheric beasts are the strangest of the flying monsters from cryptozoology. According to eyewitness reports, they are things that seem like living creatures, but they break all the usual rules that we apply to living things. They fly without the need for wings and their bodies are only semi-solid, often partially invisible to boot. Many atmospheric beast sightings were originally classified as really unusual UFO reports (in the sense of UFOs being defined as supposed alien spacecraft or machines of some other sort, not in the technical sense of being unidentified flying objects). Noted Bigfoot author Ivan T. Sanderson devoted an entire book to the theory that many UFOs are actually extremely low density animals native to the clouds. One of the most famous atmospheric beasts is the Crawfordsville Monster, sighted in Indiana in 1891, which some researchers classify as a dragon.
For those who believe, atmospheric beasts are very fragile and lightweight creatures who are either native to Earth or are aliens that came from elsewhere. If the latter view is taken, then atmospheric beasts are sometimes thought to have originated in the atmosphere of some other planet, but they can also be thought of as originating in interstellar gas clouds so that they are, in effect, aliens without a native planet, able to "swim" through space. Believers generally consider atmospheric beasts to be non-intelligent, so that even if these creatures did originate somewhere other than earth, they still don't count as sentient extraterrestrials. They're just animals.

In various eyewitness accounts, atmospheric beasts can change their density, becoming smaller, harder masses that are usually metallic in color, or they can become larger and cloudlike, even to the point of invisibility. In some reports, they may glow. Atmospheric beasts may roughly resemble whales and are sometimes called air whales or cloud beasts. Believers think that the atmospheric beasts' normal habitat is high in the air, and they might die if they ever touch the ground. Atmospheric beasts that resemble clouds may engage in behavior that is thought to be impossible for a real cloud, such as squirting a stream of horizontal water at people through "lips" or being far too mobile and animate for witnesses to believe it was just a patch of fog. The more solid kinds of atmospheric beasts may have mouths, eyes, flippers and other features, but these body parts are generally arranged and shaped in a fashion that looks utterly alien, more like an ocean invertebrate's body plan than any animal we are used to seeing on a daily basis.

It is said that when atmospheric beasts die, they fall to earth as a gelatinous mass that may resemble a green, purple, gray or iridescent jelly that evaporates into nothing within minutes, hours, or, at the longest, a few days. This is supposed to explain a type of anomalous event, pwdre ser, that puzzled scientists for some time before they decided that pwdre ser did not exist. Pwdre ser is Welsh for "rot from the stars." This phenomena is also known as gelatinous meteorites or star jelly, and reports of it come from around the world, not just from Wales. Gelatinous meteorites are not always connected with the atmospheric beast theory; they are actually easier to find among collections of Forteana that include reports of many different odd things falling from the sky.

Samples were rushed to a lab in Anchorage which quickly determined that the blob was actually just a simple plant, or algae.

"Filamentous algae" to be exact, according to University of Alaska Fairbanks marine science expert Terry Whitledge. “It means it’s just stringy,” Whitledge told the Anchorage Daily News.