This is all IMO IMG IMC and IIRIC. Be warned.
Nilmergs are made as homunculi in vats by tin dwarves with the eager assistance of lead dwarves (pipies and vessels), quicksilver dwarves (chemicals) and brass dwarves (steady heat). The process is very similar to the one used to make dwarves, and nilmergs are probably just neotenic dwarves. My private paranoia says that they were an attempt to create dwarves who were completely programmed for one single specific task which half-failed; a nilmerg is far less useful than a normal dwarf. (1)
By adding brain substance from a nilmerg whose purpose was the same as that of the nilmerg you wish to make, you 'prime' a nilmerg for that task. Their primitive minds live for that task, and are in a state of complete bliss when working on it. Strict supervision is needed to stop nilmergs from working themselves to recycling.
A gremlin is a nilmerg which becomes faulty through one of many possible glitches in the manufacturing process, all which turns the nilmerg's mind into a mirror-image of what it is supposed to be. Thus, a gremlin wants to destroy what he as a nilmerg was supposed to create, foul what he as a nilmerg was supposed to keep clean and in working order, wreck what he was supposed to repair.
Gremlins are less specific than nilmergs, though. For instance, courier nilmergs are specifically made to carry messages, but their gremlin counterparts try to disrupt all forms of communication.
Most gremlins are detected quite early in screening tests, and are re-primed to fear and loathe dwarves and their dwellings. Then they are sent out to terrorize dwarven foes. There are gremlins which makes people get lost, gremlins which cause cave-ins, gremlins which causes foundered items to break, gremlins which sneaks into studies and re-writes or destroy texts (aka 'scribe's devils'), and gremlins which causes fires to go out.
Some gremlins enter the reversed state later in the process and wreaks havoc before the special tin gremlin buster units can capture or destroy them. Some dwarven complexes are infested with them.
It is rumored eleven Gardeners know of evil Growth magic to make nilmergs into gremlins. It is also a common rumor among Octagonists that iron dwarves are really frawds, the dwarven equivalent of gremlins, intent only on destroying things, ultimately the World Machine itself.
*dwarven curse, the equivalent of the four-letter-word of RW English.
"The Owl and the Pussycat went to sea, in a beautiful pea-green boat..."
>From "The Owl and the Pussycat" by Edward Lear
Bodagatan 39, 2 tr
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