All we know about the Dark Urge is that they want to kill wantonly, that giving into the urge will potentially give you deity-like powers, and that a leprechaun thing named Sceleritas Fel has something to do with it. It's not much to go on.
I think though that we can rule some things out. First, it's not the work of fiends. There's already a cambion trying to make a deal with the party, so having another, unrelated fiend making a pact with the player would be too redundant. Also, it's not the fey, despite Sceleritas looking like a leprechaun/redcap since fey don't generally want to kill anyone and everyone. Plus, he introduces himself as your "butler", meaning even if he were a fey, he's not the one responsible for your urges.
My first instinct was that Durge is another Bhaalspawn, which would be apt since you play as a Bhaalspawn in BGs 1 and 2, and Bhaal after all was the god of murder. But I don't think that's the case. In BG1 and 2, despite being a Bhaalspawn, the player character never gets random urges to kill people (unless the player themself does, of course). Also, you never got a personal butler to assist you. So if Larian is sticking closely to the lore, Durge is not like any Bhaalspawn we've seen, so they're probably not one.
My guess? Durge gets their desire to kill from the shadowfell. The shadowfell isn't controlled by deities, but by the Dark Powers, which are enigmatic entities that are basically evil incarnate. They can pull people from other D&D settings, like Faerun, Toril, Krynn, etc into the Shadowfell and its many sub-dimensions. They also, crucially, often corrupt individuals to do their bidding. And that's what I think is happening with Durge. And unlike Fiends or Fey, the Dark Powers are prone to giving godlike power to people for being evil.
There's also etymological similarities between what we know and my theory. Dark Powers, Dark Urge, ShadowFell, Sceleritas Fel...
That's my best guess, anyway.
Last edited by Back_Stabbath; 15/07/23 02:40 PM.