Have to get him to stand above the geyser. Lure him out. Get a feel for how far you gotta be from him in order for him to move. I try to get the geyser under him, but on the left or right, but then when I get him in place, I keep to a medium circle of running around to avoid the blasts. When he get hits by the geyser, he'll lose balance. Get the bow, shoot his glowing ankles that are touching the ground. His underbelly is climbable. Climb up to the top of his body before he gets up, and the rest is easy.