When was the last time a character caught a cold or flu? Real people get them every now and again even with solid heating and dry interiors. Your characters are out in the cold and wet, and even inside is not always dry and warm. Imagine having to stop your dungeon crawl, sitting in a tight defensive position, while you all are feverish.
Arkths or Ravagers: These are large landbound crablike creatures about the size of Grizzly Bears. They live partially in the astreal plane. Their food is magic. They can sense it at huge distances. Since spells and such are hard to eat (being in motion) and magical places are the equivalent of a sea of krill to them, they are looking for magic stashed in concrete places. Their primary food source is magic items, alchemical potions, and enchantments. They do a pretty good job of mangling/ eating the physical aspect of said items in the process of chowing down. These things will be the bane of dungeons everywhere, as they will slowly eat away much of the treasure (and the magical traps... so it can be advantagous to follow these things). Note: They will attack people with highly magical natures (i.e. high magic powers). They will probably kill the person in the process of sucking out the power.
Khor are a monsterous and violent race. Within five years of being born, they grow to about half human size and are very, very inteligent. As they get older, they get larger... unfortunately they become less intelligent. After their adolecesence (about seven years), they grow to human size and are of a low human intelligence. As they age, they grow larger, slower, and stupider. Most of them end their lives 3 to 4 meters in height. Khor have been reported upto 10 meters tall, though those elder giant Khor do little but hit anything that disturbs them.
As they age they get larger, they don't seem to ever die of natural causes.
After particularly intense storm, a green glowing fungi can be found on the trees and plants. Also new monsters seem to be in the region. These storm are obviously bringing these things from other places and depositing them with the wind, rain, and goop upon the land.
The journey had been a long one and now they had entered the mountains. After an entire day spent on paths cut into the mountainside and through moss covered coniferous woods, they encounter a desperate young mountain tribal. He is searching for his beloved wife and his elder brother, both of whom he got separated from after an unsuccessful attempt to kill a cave bear. The last thing he saw was the cave bear in full pursuit of his wife. He could not help her as he had been knocked to the ground by the raging beast, and was struggling to regain full consciousness. The tribal will be clearly nervous and urges them to look for his wife during their travels. He will stay in his village a couple of miles to the north and pleads for assistance should they recover his wife, whether she be dead or alive.
On the next day of travel, they will journey upon a dim track in the forest and while they are preparing to ascend another path cut into the mountainside, they hear moans of lust from somewhere nearby. Upon closer inspection they will spy a young tribal woman in the heat of the act with an elder tribal male. They are consummating their forbidden love on the cold mountain moss, and beside them lay the skinned and slaughtered carcass of a huge bear.