Achievement unlocked when reaching the end of the game. Takes literally five minutes or less.
Start by moving to the left until you find the mammoth child. Trumpet to make it follow you. Move to the right until you reach the end. On the way there, trumpet when seeing other mammoth children, and trample towards hunters to kill them. Also trample their huts to destroy them, then go to the graveyard furthest to the right and finish the game.