Flayer Youngling
Source: Pet Battle. A brash fel orc once tried to enslave these critters as his personal soldiers. Pieces of him are still scattered across Outland. Humanoid type. These are actually in Terrokar Forest, not Hellfire Peninsula, despite what the Pet Journal says.
The Flayer Youngling is a humanoid pet battle encounter found in Terrokar Forest that you can capture for your collection.
Guide awaiting review
Travel to Razorthorn Rise
Head to Razorthorn Rise in Terrokar Forest, which sits on the border with Hellfire Peninsula. When zone merging is active, you may not see them on tracking until you cross the zone boundary.
Battle and capture Flayer Youngling
Engage Flayer Youngling pets in pet battles and weaken them until you can capture one. Hunt during off-peak hours like around 4:00 am server time when multiple spawns may be available together.
Obtain a high speed version
Seek out a Flayer Youngling with high speed stats, as this version benefits most from the Kick ability, which stuns opponents and skips their turn while also providing a free heal.
Tips
Flayer Youngling is effective against critter pets since it takes reduced damage from them as a humanoid and has access to Beast abilities like Rampage and Triple Snap that deal bonus damage to critters.
This is one of three humanoid pets obtainable through pet battles; Sporeling Sprout and Qiraji Guardling are alternatives if you need a humanoid pet for Family Reunion achievements.