It's really tricky, he sees you and you fail or if you go too far away you fail as well. There are two checkpoints hopefully (the sparkly area). After each checkpoints he goes to a blue mushroom pack and turns around for about 10 seconds on normal game time. Those are the only times he turns around.
As he gets near the pack of mushrooms, I suggest getting on normal game time if you were in accelerated or decelerated time, it helps to time better for me. Try to indicate the exact spot where he turns around in that pack, might cost you a try but it's worth. When he gets close to this spot, stick the camera on the mountain's rocky side (the left wall), not on top of it, just stick to it, otherwise you'll be too far. Then when he gets to turn around, place the camera slightly behind him but not completely behind, otherwise you might not get the timing right to go back.
When he's turned around, he'll look for you at his left, then his right (actually he still only sees in front of him so you can hide at his right side and slightly behind and it still works). He'll do this left/right pattern 3 times. At the end of the third time however, his animation will not return to it's original standing position: when he'll look at the right, you'll see him turn around again without looking in front again like the last two times. When he turns around again, place your view back where you were before he got in the mushrooms.
Now this might not work because when he'll turn around a second time, you won't see him turn around and then walk, you'll see him instantly walking in the direction he's going, but his vision box (if I can call it that way) will still follow a circular pattern, so since there is no visuals on where he's looking, the timing might be silly, almost trolling, that's why I prefer being on normal time mode. When it's at normal time, I quickly go back to the original point of view at the exact sprite I see him turned around again. When I did this with accelerated and decelerated time, it never worked since I can't figure out the right timing.
Like I said, it's going to happen two times, each after a checkpoint (sparkly area). Hope this helps
