Gremlins have a rather scandalous origin. Biologically, they are essentially genetically engineered Reekin developed by Gnomish scientists within the last hundred years or so. Psychologically, however, they've been laboriously conditioned to be averse to violence and self-determination in general. This has made them the perfect servile race for the Gnomes, so long as one ignores the heinous ethical concerns involved with 'creating' slaves for oneself through genetic and psychological manipulation.
More recently, folks in the Underkingdom have tried to distance themselves from the Gremlins origins while simultaneously retaining them as cheap labor. It's no great secret that they are the result of years of unethical thaumaturgical tinkering with the Reekin species, but individuals will go out of their way to avoid the topic whenever possible, talking circles around it without allowing themselves to admit their complicity in what is surely a serious sapient rights violation. And as long as it's not being brought up, most everyone else on the world stage seems unwilling to press the issue.
A Brewing Revolution
Unbeknownst to their creators, the Gremlins have been quietly weakening the shackles that hold them in servitude. Not only has the conditioning applied to them in decades past begun to wane over more recent generations, but some escaped Gremlins managed to end up back amongst their Reekin kin, crossbreeding and allowing a strain of the old blood to slip back into circulation undetected. By the modern age, nearly half of the Gremlin population has some small percentage of 'pure' Reekin in them again, disrupting the limitations the Gnomes instilled in them and allowing a greater degree of free - and occasionally even violent - thought.
Utilizing this new capacity to self-determinate, the Gremlins have been slowly, quietly coordinating. They've formed networks of communication, built up archives of various Gremlin 'masters', sorted by their public and private opinions on Gremlin treatment and the current status of the Gremlins under their employ, and even roped a few local Reekin populations in on their schemes, ensuring random raids on Underkingdom holds would never harm people important to them. The end goal of all of this preparation is, as one might expect, freedom. Peacefully if possible, but gained through blood if necessary. There are a few different factions within the heads of the planned revolution who have their own leanings toward or against violence, but all agree that there can be no limit to how far they will go to attain the freedom enjoyed by the rest of the world. If it comes to war, then so be it.
At the current rate of preparations and planning, the first stages of the revolution - the earliest, non-violent demonstrations of free will and a desire for the rights of full citizens of the Underkingdom - will begin within the year.
Gremlins are generally referred to as looking like 'Reekin gone soft', though this doesn't quite cover everything. In a very general sense - being bipedal, reptilian figures of short stature and a bottom-heavy physique - it's accurate, but the number of subtle differences add up rather quickly. Based primarily on the local Reekin strain, the 'Digger Drakes', Gremlins are taller than most Reekin by a fair margin, putting them nearly at the height of some Dwarves. Their muzzles and barbels are short, with rather dull tooth-ridges. The fringe of spikes along the sides of their heads flare outward and have a bit more flesh on them than most Reekin, making them appear more like large ears than reptilian horns. Their phalanges - both fingers and toes - are longer than on Reekin, making them more manually adept, while reducing the combat and utility potential of their stubby claws. Gremlins also lack the Digger Drakes' unique digging claw almost entirely, having it instead manifest as a sort of bony cuff over their wrists.
Because female Reekin are so rarely seen outside of their warrens, the Gnomish scientists who crafted the first Gremlins were unable to utilize them in their creation. However, they still needed the end results to be able to breed, so as to not need to keep laboriously crafting more over time. As such, the Gremlins are hermaphroditic, still requiring two individuals in order to breed, but with no actual distinction in sex between individuals as both carry both sets of sexual organs. It's been speculated that this is partially to blame for the Gremlins' slightly larger size and longer lifespan than the typical Reekin, as they tend somewhat upwards towards the female end of their sexual dimorphism spectrum.
The average Gremlin is quite bright, though few have an opportunity to display it. They combine the stereotypical cunning of male Reekin with the level-headedness of their females, melded together with any knowledge they manage to glean from their Gnomish and Dwarven masters. How much of this they are able or willing to utilize generally depends on how firmly their mental conditioning keeps its grip on them and how much slack they are provided to act of their own accord. Gremlins kept under close scrutiny will often play up a certain level of witlessness and naivete in order to smokescreen for their less-restricted kin.