Paleshell Crab
Source: Pet Battle. Paleshell cave crabs are said to be the tastiest variety. Perhaps that's why they're the hardest to find. Aquatic type. This is from my own personal experience, but it seems like only ONE battle pet can spawn at Castaway Cove at a time (including the upper pool at the top of the map).
The Paleshell Crab is a wild battle pet found in Undermine during The War Within, obtained by repeatedly killing Cave Crabs around Castaway Cove and Blackwater Marina until the rare Paleshell variant spawns in their place.
Guide awaiting review
Head to Castaway Cove
Travel to Castaway Cove in Undermine and begin looping the perimeter of the main pool. Confirmed spawn locations include at 68.06, 21.87 and at 68.35, 20.63 around Blackwater Marina to the north.
Kill Cave Crabs Only
Paleshell Crab is a rare spawn replacement for Cave Crab, so kill every Cave Crab battle pet you find — killing non-combat critters in the area does not affect spawns, so ignore them entirely.
Watch the Respawn Timer
Cave Crabs respawn approximately every 1.5 to 2 minutes, so keep circling the main pool and check the smaller back cove near the Darkfuse area if nothing appears after a couple of minutes.
Check the Upper Pool
The upper pool at the top of the map has very limited spawns, so make a quick stop there at at 62.94, 31.2 and at 62.12, 31.34 between loops of the main cove, as Paleshell Crab can appear there as well.
Use a Target Macro
Spam a macro using /cleartarget, /tar Cave Crab, /tar Paleshell Crab, /cleartarget, and /stopmacro in sequence while running the perimeter so you immediately detect when a Paleshell Crab spawns among the Cave Crabs.
Tips
Only one battle pet appears to be able to spawn in the area at a time, so killing Cave Crabs is the primary method of cycling toward a Paleshell Crab spawn.
A Paleshell Crab was observed spawning at 67.1, 25.8 while a Cave Crab was simultaneously up nearby, suggesting they can occasionally share the space.
