Dark Whelpling
Source: Drop. Hopes that someday it can grow up to destroy villages, just like mommy. Dragonkin type. Farmed out in Burning Steppes by the same dragons that skin Black Dragonscales.
The 
Dark Whelpling is a Classic-era companion pet that drops from Ebon Whelp in the Wetlands and Scalding Whelp in the Badlands, with an extremely low drop rate of around 0.1%.
Guide awaiting review
Farm Scalding Whelps in Badlands
Head to Lethlor Ravine in the Badlands and kill Scalding Whelps. A highly efficient cluster of whelps can be found at 61, 48.6, where they spawn in a circle close together — one player reported a Dark Whelpling drop after just 23 kills at this spot. Additional whelp locations are scattered across the ravine at 70.8, 40.3.
Farm Ebon Whelps in Wetlands
In the Wetlands, Ebon Whelps also drop the Dark Whelpling. As a bonus, the 
Tiny Crimson Whelpling can drop from every mob in the Wetlands zone, meaning you have a chance at two whelpling pets simultaneously while farming Ebon Whelps here. Whelp locations are spread across the zone at 42, 66 — 50, 75, and 46, 81.
Check the Auction House
The Dark Whelpling is tradeable and may be listed by other players on the Auction House, which can be a faster alternative to farming the 0.1% drop rate directly from Scalding Whelps or Ebon Whelps.
Tips
Both members of a duo can farm opposite sides of Lethlor Ravine simultaneously to cover more Scalding Whelps — player reports confirm that back-to-back drops are possible, even if extremely rare.
The Dark Whelpling also drops from whelps in Duskwallow Marsh, giving you an additional zone option beyond the Badlands and Wetlands.
