In folktales, trolls traditionally live under bridges. Why is that? It makes the most sense if trolls are amphibious creatures who paddle around in the water between their feasts on merchants, PCs, and billy goats.
Making all trolls amphibious makes sense of their hairless, rubbery, froggy skin and their weakness to fire. It also lets them catch some of that “Zombie Survival Guide” horror: you can’t escape from them by land or sea. In fact, trolls are much scarier on the high seas: they’re nearly invulnerable to fire under the sea and on dangerously flammable ship decks.
Get rid of the scrag, the D&D aquatic troll variant. Instead, give all trolls a swim speed and water breathing. Put troll dens near rivers, lakes, and bogs, where they can retreat, Grendel-like, when they need to regenerate for a bit.
Works well if trolls are to be monsters only. Makes them downright frightening to players who think they’ve seen “those old school monsters” and aren’t concerned about them.
Over at Tunnels & Trolls, especially Deluxe Tunnels & Trolls, various otherworld creatures are called trolls, but seem more like different species — and are often the good guys. Many are PCs.
The point, if any, is that a nomenclature can fool you. When Europeans flocked to the Americas, they brought their words with them – and used them for creatures and plants which were NOT what their names meant. (Previously “corn” meant grain of almost any sort, “buffalo” did not mean the bison, etc.)
Classic and visual example: early Conan comic by Thomas & Smith. Conan is faced with a rhino. “UNICORN!” he shouts in alarm.
It occurs to me — If all trolls are Scrags, is Honest Abe Yokum a half-troll?
It doesn’t explain the acid weakness though.
Perhaps scrags remain the salt-water variant and trolls are simply the shallow, fresh- or swamp-water variant.
The Dogpatch connection, however, DOES explain this! The Scraggs line was particularly vulnerable to Kickapoo Joy Juice, which is 30% battery acid.
@Rhenium
Actually, if Trolls are Scrags, then they only regenerate in the water, so for the most part, the “weakness” to either acid or fire doesn’t come into play if its own land. (If a Scrag gets hit by either, jumping into the water quickly will usually stop the damage before it really starts, as well as soothe its fresh burns, anyway.)
If the Scrags are already underwater, then both fire and acid will have trouble reach the trolls.
The only way it will come up is if the Scrag retreats to water, licks its wounds, and ambushes the PCs again when its healed completely-which it can’t do to 100% without week-long natural healing if it took acid damage. Which makes sense if you stop and think about how nasty aggravated fire and acid burns are.