silica

I had the same problem with the Great Gate.
When you jump on a bouncy box to get over the fence the second time you need to walk along and get all the fruit and there is also one box as well so you need to spin and jump around to find it. When you get as far as you can go behind the fence you need to go back and get the bouncy box which you used to jump over the fence and then finish the level as usual.

On Upstream there is a box with and exclamation mark on it. You have to jump on that then travel backwards till you get to the log and you will see that boxes havd appeared that you need to get.

On the Jaws of Darkness there is a hidden box that took me ages to find which is on the first platform that the blue gem takes you to. ONce you spin the boxes you go on top of the grey box and jump high and there should be a box there.

To get the first key you have to finish sunset vista and get the white gem and when you do you will also get a key, but I still havent got the second key yet!