Bloodtusk Mammoth (Non-Tameable)
Head to the Bloodtusk Mammoth's map marker to begin the hunt. It is located to the north.
Speak to the hunter there and he will tell you that the Bloodtusk Mammoth is wreaking havoc.
Get to the indicated area and follow the trail to find the mammoth.
When you find the mammoth, he will be fighting another group of hunters. Go and join the fight.
The Bloodtusk Mammoth has a LOT of HP and also hits like a truck. Take extra care that it doesn't corner you. Use fire to add a few damage per second.
When you get its HP down to a certain amount, it will run to another area. Chase it down.
In the next area, there will be big chunks of ice hanging above. You can shoot these while the mammoth is under them to cause decent damage to the mammoth. Continue dealing damage till it attempts to flee again.
In the last area, the mammoth will no longer run away. So deal all your damage to it now. Again, use fire for additional damage. If you have resources, use the traps as well.
When its HP is gone, it will drop down. Too bad it isn't tameable. So just kill it to end its suffering.
After the lengthy animation of killing the mammoth, the mission is now complete and gives you massive amounts of XP.