I'm surprised we don't yet have salamanders.
But don't just make them fiery lizards, do something interesting.
A high body temp, immune to lava and fire, melts the tile they are on, can cross shallow water by evaporating it. Fire breath, too.
Make them have a hive/pack mentality, and castes, like antmen. So you have Hunter/Defender Salamanders (larger, male, defend the rest of them), Working Salamanders (female, children, 'working' explained in next paragraph), and named Hierarch Salamanders (male mostly, much larger and hotter, generally tougher). They aren't a civilisation, like the ants, but some obvious caste system and working together would be a nice little bit of information.
If creatures can burrow in the future, or if the underground can generate small, winding paths with little holes off them for 'living', this is where the salamanders live. Normally AROUND the outside of a magma pipe, over a few z-levels, and this is dug out by the shovel-headed workers (in reality, it was pre-generated, obviously, since burrowing pathfinding must be nigh-on impossible). The arrow-headed males to the fighting, unless the workers and Hierarchs are provoked. Hierarch Salamanders are only a little better than dragons in terms of ease to kill; if weapon degredation is included, using a wooden or inferior metal would cause it to burn/warp/melt/etc. The size of workers is a little smaller than a donkey's torso, hunters maybe a cow torso, and Hierarchs are closer to Ankylosaur size. They're a real bitch when provoked.
One reward for killing them could be some kind of lukewarm glue, you get a 5-15 globs per Salamander, which can be used to 'decorate' weapons. When this weapon is used, the glue essentially 'magically' (until we have matches) ignites, giving the enemy fire damage, too.
You rikey?
Also, as just another enemy, where are the tree people? Worshipped by elves, a match for a Bronze Colossus, able to deconstruct? 'Catapult' rocks? They come to your fort after x number of trees have been cut down, or with an elf siege.