The Purvis swamp varies with the seasons. In the spring and autumm it is at it’s most foul and marshy, and even the Sproggans sail on coracles and small boats rather then try and walk through it. Swarms of biting insects are a problem, but not to the Sproggans, as Sproggan blood poisons them, so after a mosquito or two has died as a result, the rest keep well away.
In the winter the insect swarms are gone, and the swamp is cold and can be icy on the edges. But it is in the hot summers that the swamp is special. With the exception of a few rivers that are allways deep even in the hottest weather, the outer layer of mud dries up and cracks. The Sproggans can walk across this with ease, but other races find out, often very unpleasently, that only the outer edges of the swamp are dry enough to bear their weight.
Those who penetrate too far without taking proper preperations first, find that the muddy crust cracks under their feet, trapping them in the ooze and leaving them at the mercy of the Sproggans. Those who are long term friends of these goblinoid race will be rescued, but anyone who has given them a hard time will be unable to stop them from cutting their throats, before looting their bodies and letting them sink into the mire.
There are Sproggan tales of how an Ogre warband tried to take vengence on the Sproggans for some reason, and invaded their swamp in the dry season. Their heavy bodies sank up to the shoulders in the mud, leaving them helplessly stuck, much to Sproggan amusement.
The mud will heal cuts, but it also gets into the pores and causes musle wastage if not quickly cleaned off, something which the Sproggan body is immune to.
The Sproggans themselves live in huts on the branches of the mangrove trees that live in the swamp. The ladders will crack if a non-Sproggan tries to climb up them, and the trees themselves are very hard to cut down.