Scrags are aquatic trolls that harass travelers on rivers and at sea. Their coloration befits their aquatic lifestyles, ranging in colors of blue and green. This category includes both "freshwater" and "marine" scrags.
Combat
Scrags are devious predators, leaving valuables near their lairs while they hide beneath the sand, under an embankment, or buried in the mud nearby. When a person comes to grab the gems or cois the scrag has lain down, they strike. They are also a fan of residing near civilization, beneath bridges and docks, preying on children, lone travelers, drunks, and other easy victims. They have learned that boats often contain more than one choice prey item, and so have learned to tangle them, lurking in the water, and reaching up to grab from the floating buffet as the hapless riders try to free the boat.
A quirk about scrags is that they cannot regenerate unless they are immersed in their waters, and they cannot breathe for long outside of an aquatic environment. Though they raid land, these raids are likely to be short, as they are fully aquatic creatures.
Society
Some scrags set up toll systems near docks or bridges that they frequent, gaining food in exchange for safe passage. Their packs have leaders just like their land-bound cousins.
Ice Trolls
Scrags in polar environments live amongst glaciers and shifting icebergs. Perhaps the most cunning of trolls, they have been known to keep humanoids as livestock, letting them live long enough to pick them off when they are "big enough." Like other scrags, they must be immersed in water to regenerate, but they are clever, and prefer to fight using weapons, picking off the weakest members of the party first. They also are more social, congregating in bigger groups. They are unaffected by cold, but fire and acid shut down the ice trolls' marginal regeneration nicely, just as in other trolls.