Scorpling
From Freka Bloodaxe. Despite its snapping claws and venom-dripping tail, it is the bite of the diminutive scorpling that is the greatest threat. Beast type. These, along with many of the other rarer battle pet spawns, seem to work much like fishing nodes--where only a set amount of battle pets can be on the map at one time.
The Scorpling is a wild battle pet found in the Blasted Lands, spawning at level 16 on top of the mesa east of the Dark Portal.
Guide awaiting review
Travel to Blasted Lands
Head to the Blasted Lands and look for the Scorpling on top of the mesa to the east of the Dark Portal at 65.2, 61.8.
Force rare pet spawns
Wild pets in a zone share a limited spawn pool, so battling and catching other wild pets in the area frees up slots and increases the likelihood of a Scorpling appearing. If the zone has low player activity, spawns will refresh slowly, so actively battling nearby critters is the fastest way to cycle the pool.
Choose your Scorpling breed
The Scorpling is available in B/B, H/S, and P/S breeds, so inspect the pet's stats before capturing to lock in the breed that fits your preferred playstyle.
Alternative: Buy from Freka Bloodaxe
If you prefer to skip the wild hunt, Freka Bloodaxe in Icecrown at 76.4, 24.2 sells the Scorpling directly.