No cave in use (it think you are looking at at water spot ). He is pretty much out in the open. Thales, I don't know where the crayon is. The only thing I could call close would be the orange feather duster but that is bottom left. You are in the right area with the middle left though. I really did not think this one was hard. I almost didn't post it because, to me, he shows up pretty clearly once you click on the photo. He is much less evident to the naked eye when he does not want to be seen.
Then I think you actually found the "faux octopus" rock. There are several in this tank complete with "eyes" and suckers There is a "big old arrow" on his thread linked to in the original post.
CG, that is why I thought it was too easy. With the eyes he does not show up that way but the way my camera enhances colors a little (especially if you direct the focus to one spot) he shows up more in the picture than he does in life. This one has been invisibly in front of us so many times we challenge the other to find him when he decides to merge with the rock. He is especially good at looking like the fuzzy algae that grows near the top of the tank.