Quicksand

Quicksand was a naturally-occurring terrain feature and hazard made up of sand or dirt that took a near-liquid consistency.

Properties
Found in swamps, bogs, and low-lying wet areas, quicksand was a volume of waterlogged, near-liquid sand or dirt. Appearing innocuously as a patch of ground up to across with little to no undergrowth, quicksand was hard to notice for inexperienced or inattentive creatures. A creature such as a human could unwittingly blunder into the quicksand, at which point they would begin sinking through the ground.

Sand-based quicksand was a treacherously thin mixture of water and sand, causing the victim to sink rapidly if they could not keep calm and tread water. Although it was possible to escape without drowning, the effort of swimming and climbing out of sandy water was exhausting, so being rescued by others using a pole or branch (or a strong, experienced swimmer) was highly recommended.

Earthy, dirt-based quicksand was effectively a pit of thick mud, and could be water-treaded and swam out of with relative ease as long as the victim wasn't exhausted, overly encumbered, or injured. Mudslides formed similar hazards, potentially washing victims along into an area filled with mud.

In deserts, quicksand formed from large amounts of fine, powdery sand that gathered in depressions. Like watery quicksand, it could swallow people and animals easily if they were encumbered or responded with panicked movements that dug them in deeper.

The Realms

 * Memnon's presence in the Calim Desert caused the ground to break apart into fine sand, spontaneously generating dry quicksand.
 * Glaun Bog in Tasseldale was a morass of quicksand and sinkholes.
 * The city of Hawa used disguised quicksand pits to defend the city from attackers.
 * The swamps of Kutuk Valley had an inordinate amount of quicksand.
 * The marshes near Lathtarl's Lantern swallowed up Ring Tredarath and his retinue in its quicksand thanks to their heavy loads of treasure.
 * The depths of the Lurkwood were said to be home to lethal quicksand, deterring potential explorers.
 * The Marsh of Chelimber had uncommonly large amounts of quicksand.
 * The Mere of Dead Men had a great amount of quicksand.
 * The stagnant swamps of the Moonshae Isles had a very high prevalence of quicksand.
 * The Moss was an artificial swamp of Netheril, filled with quicksand and lethal gas pockets.
 * The fortress of Opawangchicheng lay within a swamp with sinkholes and quicksand.
 * Quicksand lay in the heart of Taglan's Bones.
 * Shibi Swamp was full of dangerous quicksand.
 * The Vast Swamp had much quicksand and other forms of hazards in its depths.
 * The Zehoarast Floodplains were marked with quicksand from the regular flooding.
 * The Fireplace Level of Undermountain had a sand pit trap that worked like quicksand.

Other Planes

 * Among other lethal or unpleasant features, Avernus of the Nine Hells had pits of quicksand.
 * Othrys of Carceri had bogs and quicksand that extended thousands of feet deep.
 * Quicksand was a major feature of the Para-Elemental Plane of Ooze, especially near the border of the Plane of Water.
 * The plane of Qui had extremely wet periods in its seasonal cycle, with much of it regularly turning to quicksand.
 * Zrintor of the Abyss was a marsh dotted with "quicksalt" hazards.

Creatures

 * Adult amethyst dragons could walk on quicksand or any other surface without disturbing it.
 * Ash giant shamans created masses of loose ash that acted like quicksand.
 * Basidironds would sometimes make prey hallucinate that they were trapped in quicksand.
 * Brain spiders used their psionic abilities to trick prey into quicksand and other hazards.
 * Camels were usually able to swim and thrash their way across quicksand, even when laden with cargo and a rider.
 * Gibbering mouthers preferred quicksand, and could move quickly through it. They used their powers to liquify earth and stone into a thick quicksand.
 * Groundsquids produced a greenish jelly that trapped prey in a pit.
 * Hags often altered the landscape around their lairs to become more inhospitable, including creating quicksand.
 * Tortles were buoyant enough to float on water or quicksand.
 * Retchenbeast drakes looked for carrion to eat in quicksand.
 * Will-o'-wisps were fond of leading victims into quicksand.

Spells & Magic

 * Sand of sinking was a magical sand that turned solid ground into quicksand. Conversely, solid sand turned unstable ground such as quicksand into a solid mass.
 * Detect snares and pits informed the caster of the presence of quicksand.
 * Dusting the rock used some dried quicksand as a material component.
 * Immunity to adherence protected the caster from being stuck in quicksand.
 * Protection from earth and stone protected the caster from quicksand, mud pits, and similar threats.
 * Sandswallow caused a large area of quicksand or other soft ground to collapse inward, swallowing foes.
 * Transmute mud to rock turned an area of quicksand or mud into a brittle stone.
 * Water walk allowed the caster to walk across quicksand and other semi-liquid surfaces.