Rebuilt Mechanical Spider
Drops from Mechantula. Anyone serious about using a mechanical spider in battle knows that you need to buy replacement legs in bulk. Those things are fragile. Mechanical type. / is a pet made from gathering several items. The materials for can only be found as Horde.
The 
Rebuilt Mechanical Spider is a Horde-only craftable battle pet assembled from three materials dropped during Faction Assault events in Vol'dun.
Guide awaiting review
Wait for Vol'dun Assault
The materials for Rebuilt Mechanical Spider can only be obtained when a Faction Assault is active in Vol'dun. The Vol'dun assault rotates approximately every 4.75 days, lasting 7 hours each time.
Help Dookthar Win the Fight
Head to the bridge in Vol'dun where Dookthar the Destroyer and Arachni battle. To help your faction's bot win, kill bugs in the area until you collect enough to fill Dookthar's energy bar, then turn them in while the bot is recharging. Your faction's bot must win for you to loot the cache.
Loot the Cache
After Dookthar the Destroyer wins, loot the cache on the bridge. It contains one of three materials: 
Handful of Glass Spider Eyes, 
Steel-Plated Arachnid Exoskeleton, or 
Mecha-Spinneret. You can only loot the cache once per invasion, and since items are unique, collecting all three takes a minimum of three separate Vol'dun assaults.
Craft or Buy the Pet
Once you have all three materials, combine them to create the Rebuilt Mechanical Spider. Because the pet can be caged, it is also available for purchase from other players on the Auction House if you prefer not to farm the assaults yourself.
Tips
You do not need the Vol'dun world quest to be active — simply being present on the bridge during an active Vol'dun Faction Assault is enough to participate and loot the cache.
On servers dominated by one faction, turn in your salt to Dookthar while no opposing players are around to avoid your bot losing the fight.
The Alliance equivalent of this pet is the
Rebuilt Gorilla Bot, obtained through the same event mechanic but in Alliance-controlled zones.
