neither types are actually true Kobolds.
Rumpelstiltskin was a true Kobold. They're little people of Germanic lore who did household chores, or inhabited mines, who were know to pull mischevious pranks when insulted.
Like making veins apparently of copper/silver be of another material, i.e. an ore of the to-be-isolated-later element colbalt, which was useless (in the context of copper and silver mining, although mostly to do with the usually also-present Arsenic compounds 'poisoning' the usual smelting processes, in the true chemical sense.).
Although cobalt
does have uses (in the moderm world), e.g. one of the few ferromagnetic materials ("NICS" was the mnemonic I had to remember, a long time ago: Nickle, Iron, Cobalt and Steel... but there are others, and 'Steel' is a bit of a cheat and not
entirely accurate). One use is batteries, while certain alloys of cobalt give materials suitable for jet-engine blades. We know these days that cobalt is necessary (in very small trace quantities) to allow Vitamin B12 to be introduced into the food-chain. And traditionally cobalt-based pigments gave a set of blue colourations to both glass and to paints themselves.
Kobolds, therefore, should maybe be blue in colour, small, troublesome to the normal working of a fortresss, I would hesitate to also demand that they be extremely heat-/force-resistant. But they should be thought capable of carrying picks and hauling on ropes, or miniature versions of them, in their own mining efforts (echoing the "knocker" spirits of the Cornish tin-mines) and thus be little humanoids. Probably with contemporary peasant-/miner-like clothing.
(And then there's the nautical kobold, that seems to be a far more helpful little sprite... Depending on whether you treat them nice, I suppose, but treating the mine-living sprite nice often made them turn even
more useful ore to its useless equivalent.
)
But... who says that Dwarfworld Kobolds have to be anything like Roundworld ones traditionally are...