The Great Beast (Jayma the Hunter) | Walkthrough Far Cry Primal Guide

Provoke the mammoth so that he will follow you.

Go to the hunters and then walk down the river in search for a mammoth. Attack it once it is tracked (the safest way is by using arrow from as far away as possible) and return to the hunters. To avoid being killed by the mammoth on the way back, you can ride one of your pets or send your animal at the target to distract the giant animal.

Run around the stone circle. The mammoth will be attacked by your allies and you will avoid his deadly charges.

Once you reach the destination, the mammoth will focus mostly on you. Avoid his attacks and charges and deal as much damage as possible with arrows and thrown spears. Your tribesmen will also attack the mammoth, so focus mostly on staying alive for long enough. Use the help of your animal and/or traps to kill the mammoth faster. It is a good idea to run around the stone circle with the fire. This will reduce the chance for the mammoth to deal damage to you. It will take some time, but finally the mammoth will drop dead.