Tranquil Mechanical Yeti
From Tranquil Mechanical Yeti. This clever toy is equipped with a secret switch to disable its 'tranquil' mode. Luckily, even the engineers who built it don't know how to find it. Mechanical type. Given that the pet is now a battle pet, I'd say the Engineers found the switch disabling "tranquil" mode.
The 
Tranquil Mechanical Yeti is a non-combat Engineering pet crafted via a schematic unlocked by completing a chain of quests in Winterspring, culminating with Umi Rumplesnicker.
Guide awaiting review
Start the Quest Chain
Speak with Lilith the Lithe in Everlook, Winterspring, and pick up Hammer Time. She will direct you to Deez Rocksnitch to begin the chain.
Complete Deez Rocksnitch Quests
Complete Rubble Trouble and Boulder Delivery for Deez Rocksnitch, then return to Lilith to finish Boulder Delivery.
Complete Kilram's Quest Line
Pick up Kilram's Boast from Kilram, complete Chop Chop and Tree Delivery, then speak to Seril Scourgebane to get Seril's Boast.
Unlock Umi Rumplesnicker Quests
After getting Seril's Boast and speaking to Deez Rocksnitch for the follow-up, three quests will appear on Umi Rumplesnicker — pick up Are We There, Yeti? and The Perfect Horns.
Complete the Yeti Quests
Finish Are We There, Yeti?, The Perfect Horns, and Yetiphobia for Umi Rumplesnicker. Upon completing the final quest, you will be rewarded with the schematic to craft the Tranquil Mechanical Yeti.
Gather Materials and Craft
To craft the Tranquil Mechanical Yeti, gather the following materials: 1 Cured Rugged Hide, 12 Thorium Bars, 4 Runecloths, 2 Globes of Water, 4 Truesilver Bars, 4 Elemental Earths, 2 Elemental Airs, and 
1 Gold Bar.
Tips
The Tranquil Mechanical Yeti crafted via Engineering is a non-combat pet and deals no damage, unlike the version received as a quest reward.
The schematic can be learned at 265 Engineering, so you do not need a maxed skill to unlock it.
You do not need to complete the Deez Rocksnitch quest Fresh from the Hills — once Umi Rumplesnicker's three quests appear, you can drop it and proceed directly with her chain.
