The Ocadian PitFiend is a colony creature, where several different lifeforms combine together.
1) On the surface there are what appears to be shrubs. They are actually two different plants living together. One is Brycanthis, which produces a low woody shrub, the other Sochrin Vines, primitive relatives to Treller Vines. Combined, they make a low woody shrub with green leaves and small red flowers. Neither of these plants should be able to survive in this environment due to soil and water requirements, but as part of the colony, they can.
2) Deeply, there is Ocadian Fungi. The giant subsand relatives to the mushshooms can grow to huge sizes, encompassing several acres underground. They are just under the heat level (where the sun’s warmth no longer warms the sand/ soil). They provide liquid and stability for the PitFiend.
3) In the Middle combines three creatures. Ocadian SandCoral (or a variation of) is the backbone of the creature. These small creatures eat organics in the sand, protecting themselves from heat and predators by creating small shells of silicon… thus creating a coral. They create the stable foundation for the plants to root to and the Pitfiend to grow from. It is unclear if it is two or three kinds of microplants that make up the Fiend Proper. One plant produces “spoors” that stun and can immobilize creatures once stimulated (stepped on or agitated by chemical signals produced by the bush plants being disturbed). In addition the spoors begin the digestive properties. They grow on the surface out of the SandCoral. The colonies of Sand Anemones will shoot their “once in a life cycle” tentacle… drawing the creature into the pit. (they will then reproduce, drawing upon nutrients from the caustic goo inside the bulb). Inside the bulb of the fiend (held together by coral and the plant roots) is a number of microplants and animals that digest flesh quickly and even can break down bone and metals. The goo inside the bulb can completely digest a human in about four hours, passing nutrients and water out of the bulb to the rest of the colony. In fact they are so acidic that they must remove the water quickly less it becomes so unacidic that they die. One of the microcolonies of the goo does nothing but that.
The Yak was attracted to really nice looking plants that should not be able to survive here in the desert. It seems to act drunk, unsteady. It is slowed and stunned by breathing in spoors. Then tentacles shoot out, drawing its prey underground. If small enough, it disappears completely under the sand… but the Yak is too big, it appears to slowly sink into the sand among the nice bushy plants.
Even if you rescue someone from the bulb, part of their body will be dissolved and will be infected by a number of microbes that will continue to try and digest the victim. Even being near the plant is dangerous, as inhalation of the spoors will lead to tiredness, fatigue, paralysis, and begin to break down the lungs and wet tissues they touched, causing bleeding from the eyes, nose, and lung… as they are slowly digested by the spoors.
In fact, the rizone (mushroom) element counts on things getting away… they will then decompose and feed both it and the PitFiend.
Spoors will be an issue for people, but by the time people realize someone has been infected, not only have all of you have been effected, but much damage has already been done. The PitFiend wound (swallowed) can be stopped by the “Old Ranger Trick” of swabbing the wound with a honey and water mixture. Magic can resolve some of it, but there will be 1-6 “diseases”/ parasites that will need to be removed (thus 1-6 spells of removal). Also one of the microflora put out a strong anti-magic field (for a microanimal) so it is difficult to resolve anyways. After all, it is the most dangerous creature in the desert. It can kill from a distance, it can kill you if you escape, and it will make you “gone” if you stray near it.
The only thing that gives this creature away are the innocent shrubs that are somewhat out of place and the caustic smell that bubbles up if it is digesting something.