Twilight Spider
Drops from Mother Smolderweb. Twisted by the Twilight Hammer's dark magic, these sinister critters are known to feed on their own young. Beast type. Found it in Azshara. It joined as a second pet when I was fighting with a squirrel.
The Twilight Spider is a wild pet found in Azshara, twisted by the Twilight Hammer's dark magic, and can be captured by engaging local pets in battle until one joins as a secondary combatant.
Guide awaiting review
Travel to Azshara
Head to Azshara and begin battling wild pets in the area. The Twilight Spider does not appear until you start engaging other pets.
Battle Level 5 Squirrels
Seek out and battle level 5 or higher Squirrels specifically. After fighting several level 5 Squirrels, a Twilight Spider will join the battle as the second pet in the encounter.
Capture the Twilight Spider
Once the Twilight Spider appears as the secondary pet, reduce its health and use a Pet Trap to capture it. Be aware that wild-caught specimens can be of poor quality, with stats such as 250 health, 36 power, and 36 speed.
Tips
Only wild pets at level 5 and above call a second pet into battle, so targeting lower-level pets will not trigger the Twilight Spider to appear.
At max level, the Twilight Spider can solo most wild critter-based battle pet groups using Brittle Webbing, Leech Life, and Strike, making it effective for leveling weaker pets by bringing them in to attack once before swapping in the Twilight Spider to finish the fight.