I think I figured out everything the fanart folder mentioned. (Pressing W and Z/Enter at the same time when near water so I can jump repeatably, learning how to get the hidden item, etc.), but I can't think of a good route that doesn't make me jump directly into a trigger.
A path drawn through the official game map or a video would be appreciated. :)
Update: Ok, I THINK I got it, but I think I went too far, and got stuck inside a tree. Oh well. Still can't get to the box, though.
Update 2: OH MY GOD I DID IT YES... and I got stuck on the part immediately after I jumped off.
Update 3: Got past the monster, sold the amulet, and restored the portable menu. Now what?