A Gargantuan Yeti - Act 3 Side Quest
Start Location: Shangshung Village
Quest Location: Tsongmo Ice Caverns
Objective: Defeat the Gargantuan Yeti
This quest begins by speaking with Pasang Do-Ma who is found in Shangshung Village, the first real town you come across in Act 3. Much like many other quests in Titan Quest, you do not actually need to speak with this person to complete it. When you defeat the Gargantuan Yeti whether or not you have the quest doesn't matter, it will complete and give you the reward.
Completion of this quest will give you a permanent reward/boost for your character, +100% Health for all pets that you have. You'll receive this reward for every difficulty you complete the quest on, giving your pets a total bosot of 300% once you've beaten all difficulties.
You can find the Gargantuan Yeti inside of the Tsongmo Ice Caverns; you'll pass right through this cave while traveling from the Western Silk Road to the Eastern Silk Road during the main story quests.
Boss Strategy: The most important piece of information I can give you for beating the Gargantuan Yeti is to dodge the ice breath. It will freeze you for a couple seconds which will give the Yeti plenty of time to beat on you. He has an ice nova attack too that slows anyone who gets hit with it but it isn't nearly as deadly as the ice breath. In the screenshot I have of the Yeti he's casting the ice breath attack if you'd like to see what it looks like.
Note: When you log back into the game for the first time after completing this quest (and all of the other quests that grant permanent rewards) it will give you a pop up like you're being granted the reward a second time. This is actually not the case, you will not be granted the reward a second time.