From Hellgatewiki.com

Darkspawn, Imps, and Gremlins are different types of the same base monster; identical except for their coloration and possibly their AI. Since it's often impossible to tell them apart in screenshots, and they'll probably only be differentiated by stats in the final game anyway, we're simply calling them all Darklings at this point, and sticking all the basic clan info on this page, for easier reference. See the Diabolist, Sniper, Trooper, and Scout pages for more particulars about each type of demon. Here are the official descriptions for each clan.

Darkspawn
The Darkspawn are a faction within the Primus caste that have a fascination and affinity for melding demonic magic with technology. They are insatiable in their search for the new and unknown, so they often roam the streets and tunnels of London looking for caches of items or - better yet - adventurers with powerful gear.

The Darkspawn not only craft their own equipment, but can also use any that they find during their patrols. It is not uncommon to see one wielding weapons of human design that have been separated from their original owners.

There are several distinct groups within the Darkspawn that are identified by both their specializations and their size and markings. Knowing their individual strengths and weaknesses is vital for an optimal chance of surviving an encounter.

Gremlins
Gremlins gained their moniker for their malevolently mischievous nature as opposed to any resemblance to the cute pranksters many associate with the name. They have been known to raid even the most heavily guarded facilities in order to corrupt or steal the machinery that is kept there and delight in using the weapons of man against them, favoring them over ones of their own crafting. The eerie blue glow that emanates from between the cuts in their skin reflects the spectral forces from where they draw their power.

Imps
These are the lowest of the Darkspawn clans. The cracks in their naturally tough hides reveal the essence of brimstone that drives them to battle and hints at their strengths in regards to damage and defense.

Each clan is comprised of four types of demons: shaman Diabolists, melee fighting Troopers, wandering Scouts, and ranged attacking Snipers. Diabolists are tall and skinny and look very distinctive. The three servant types are identical in appeareance, except for their weapons. Troopers wield melee weapons, usually swords, while scouts and snipers both use ranged weapons. There is no way to tell snipers from scouts, at least not from basic screenshots.

See the individual demon pages for more details about the Diabolists, Troopers, Scouts, and Snipers that make up the Darkspawn, Gremlin, and Imp families.

Community Day Update

Flux, admin of the Unofficial HGL Site, reported on Darkspawn after some HGL play time during the 2007 Community Day event. (Registration required to read Flux's full four-page mega report.)

Darkspawn were common by clvl 6, and they're easy early on. You don't get big mixed packs with a Diabolist to spur them on at that stage in the game; just scattered scouts or snipers, who aren't too hard to kill one on one. The snipers I saw were not firing very much either; just a shot or two when they first saw me, and then their AI had them kind of milling around while I killed other monsters and closed on them. I'm sure they'll be a lot more efficient later in the game; the ones seen in gameplay movies are pretty fierce.