Quicksand falls like sand or gravel when unsupported and any mob unfortunate enough to fall in is doomed unless they can dig themselves out fast enough. It is generated rarely in jungles, frequently in swamps and on beaches. It can also be crafted for a yield of two.
This can be used for traps of all sorts, defenses, mazes etc. It only smothers tall mobs if it is at least 2 blocks deep. It also damps explosions like water.
Dry quicksand is quicksand’s desert counterpart. It only generates in deserts and is non-solid, meaning you just fall into it. It is easier to get out of, but also easier to stumble into. Since it looks like regular sand, it can be used for sneaky traps and secret entrances! It can also be crafted, yielding two.