Instructions
Go to Lowtown and enter Old Dalan's Place by the Southgate.
Find Koqmihn, who is on the floor near a table. Speak to him and he will talk about a location deep in the snow-covered forest.
Travel to this place--the Edge of Reason in Feywood. Teleport to Giruvegan, then walk to Feywood.
Wander around the Edge of Reason to induce enemy attacks. You must clear this area of all of the enemies to make the Behemoth King appear. Walk around until enemies stop attacking you. Head to the nearby Ice Field of Clearsight once they do and repeat this process.
Head back to the Edge of Reason and go to the center section in the south. Wait for the Behemoth King to appear.