As such a thing they require little in the way of goods or trade, and so do not parley with neighboring villages and kingdoms in these matters. Indeed their swift and gurgling arrival in the thick forests around Seacastle have given them a ghostlike reputation among many neighboring cultures, and a reverent near-worship. This is helped by the "singing" of the Melt, undulating their surface forms and forming spires and loops, modulating the shape and sound of the wind passing over the mouth of Seacastle, a moan which is heard for several days' ride at night. Melt, however, are pretty vulnerable to attack, and wounding one in their home wounds them all. For these reasons they venture out to other cities and towns seeking treaty for peace or to scare people into submission. Many, having done so, find they enjoy being "alone" and take to the pleasures, diversions, and chemical interactions of the world with gusto.
It's hard to interact with a pool, a column of bright orange or green phlegm, or a wave rolling down the street. In order to interact with the world they need vessels, and in order to interact with humanoid society they need humanoid vessels. This usually, but not always, means the dead, either worming their way into an unused corpse or wrapping themselves on an ancient, stripped-bare skeleton. There are Melt who are known to cohabitate, sharing the space of a humanoid form with its original owner, removing its presence from time to time so that being can have some privacy or autonomy. This is an...intimate relationship, so it requires a real sympathy on all levels between the two parties. Trying to force this relationship leads to a dead body being driven around by the Melt like a car.
Should their humanoid form (which has half the Melt's HP) be destroyed without killing the Melt in the process, the Melt will be left unable to directly interact with much of their surroundings, though still 100% aware of the sights, sounds, and flavors around them. They can flow around and follow their friends until the find a new host form. A wounded and scrambling Melt is usually a dead Melt, however, so Melt adventurers usually have an understanding with their fellows for these emergency contingencies.
Melt may swap forms intentionally once per day without exhausting themselves, or twice per day if they take no other strenuous action. Melt may attempt to take over a host as an attack in this fashion but, if they are resisted, this surely endangers their lives. It is a last-ditch effort at best, and not all bodies are created equal. More powerful forms may resist the Melt's intrusion, and the act of infiltration may be fatal itself.
Melt are an ancient race and if they are not killed a Melt will live forever. They will flow over our empty world and ride the skeletons of atomic super ants. But for now they slink through bazaars on others' bones.