Once you gain control of Takkar, crouch and follow the group’s leader, Dalso. As he moves, stay right behind him to remain undetected by the Mammoths. When he stops, you stop; when he goes, you go. Eventually, your group surrounds a small Mammoth, but a larger one keeps you from attacking right away.
Wait until you receive the signal to go and then sprint toward your prey. The other tribesmen are equipped with bows, while you hold two spears. The spear offers two attacks; get in close and press the Quick Attack button for a simple stab or hold the Aim button while pressing Quick Attack to throw the spear. The latter is much more effective, but once you throw both projectiles, you must recover them from your target—or the ground if you miss.
Jump to the side when the animal charges to avoid taking damage. If you are hit, sprint away from the beast and hold the Heal button to recover health. Continue to attack the Mammoth until it charges through the nearby bramble. Follow it up the hill and wait for Dalso to tell you to kill it.