Black Lamb
From Corporal Arthur Flew. Offspring of the black sheep, the black lamb is only found in the forests of Elwynn. Critter type. Note: If you caught one before patch 5.2, it will NOT count retroactively toward the Eastern Kingdoms Safari achievement.
The Black Lamb is a wild critter pet found only in Elwynn Forest, obtained by capturing it in the wild.
Guide awaiting review
Fly Circles Through Elwynn
The Black Lamb spawns throughout Elwynn Forest at roughly a 1-in-5 rate among other critters. Fly circuits around the entire zone and engage every pet you see that isn't a Frog, as killing non-Black-Lamb spawns forces new ones to appear.
Prepare a Low-Level Capture Team
Black Lambs spawn at levels 1–3, so bring a low-level or weak pet to avoid accidentally killing them before you can capture, since there is no way to capture with a high-level pet dealing full damage to a level 1–3 critter.
Check Quality Before Capturing
After initiating combat, check the critter's health to estimate quality — higher health generally indicates better quality. The Black Lamb can be caught as a Rare without needing a battle stone, and it offers better breed options than the Elwynn Lamb.
Re-Catch for Achievement Credit
If you caught a Black Lamb before patch 5.2, it will not count retroactively toward the Eastern Kingdoms Safari achievement, so you must catch a new one for it to register.
Tips
The Black Lamb has identical abilities to the Elwynn Lamb, but unlike the Elwynn Lamb which is only available in Uncommon at breed B/B, the Black Lamb can be obtained as a Rare with better breed options.