This video covers the fourth level ("Act 4: The Level Factory") in the METAL GEAR SOLID® Premium Level Kit for LittleBIGPlanet. I Ace and collect all of the currently accessible Goodies for this level.
This recording will indirectly show you how to get the Diamond Hunter Trophy. (Note that the Trophy notification does NOT pop up because I already had that Trophy.) In addition to getting that cosmetic reward for shooting the five diamonds, shooting them also unlocks some caches at the end of the level containing a Key and some Goodies. Two of the diamonds (the first and third) are very conspicuous. Another two (the second and fourth) requite some minimal exploration. The last is the trickiest and can easily be overlooked. You need to launch out of the Sack Cannon as low and as horizontal as you can in order to reach an otherwise inaccessible area with the fifth and final diamond.
It may look like I skipped an early area to the left, but I didn't. That leads to a Sticker Switch and I currently lack the prerequisite Sticker.
I had a couple of close calls on the elevator ride sequence, but I fortunately made it through without dying. Plasma balls and hit detection can be a real pain sometimes, but I got lucky this time.
Now that I have the Gekko Crouching 1 Sticker, I revisit "Act 4: The Level Factory" in the METAL GEAR SOLID® Premium Level Kit for LittleBIGPlanet to pick up the rewards from the respective Sticker Switch.