This quest is not available in game.
Take Umi's Mechanical Yeti and scare her friends with it:
Legacki in Everlook (Winterspring)
Sprinkle in Gadgetzan (Tanaris)
Quixxil in Marshal's Refuge (Un'Goro Crater)
When you are done, bring the Mechanical Yeti back to Umi.
It's all ready, <name>!
Now, I sent some mail to my friends already, telling them that I have a surprise for them. This is where you come in!
I'm going to give you my mechanical yeti, and you need to surprise them by paying each of my friends a visit, turning the yeti on and sending it towards them.
Once you have shown Legacki in Everlook, Sprinkle in Gadgetzan, and Quixxil in Marshal's Refuge, come back and tell me what happened!
Please bring my yeti back to me then, too.