i belive no one can reach the hidden key, the place is to tight to the avatar pass it. try testing your levels before posting it
i made a lot of mistakes too but not testing a level?

NEVER

In your avatar you say you are a professional?! you know you suck at N and mapping I hope

but this was just terrible, keep this in mind while mapping:

1. No spamming of objects;
2. No hiding objects EVER;
3. Don't overdo enemies, often 1/2 well placed thwumps can do the job of 10;
4. Don't put in unnecessary objects such as the gold/mines you got spammed in the little blocks;
5. Remember that sometimes a simple map is better than a really complex one;
6. Playtest THOROUGHLY before you publish.

Thats all I have to stay, there is a lot more to remember whilst mapping but if you follow what i said your maps will end up a lot better.

Cluttering and spamming useless mines, aesthetics look bad, hidden objects and it isn't even possible because of the switch on the top left under the place where the player.
N/R