When your in the place with the big water fall ( troll hole ) theres a water fall go on the vine and jump threw it.

But keep going up the green slimy thing jump up it then.

Look around you might see a platform with the key ( platform is the thing that hold it ) you might also see the two coconuts there ( brown things with blue in midle ).

Don't smash them jump on them then jumo on the platform now go to the troll cave ( where ever that is I am stuck there too ) there you go you got the key.

Make sure you let him go around the corner, then take of you're ring and let it refill. Don't worry he dosn't go back.

But don't try to get ahead of him, he will catch you even with the ring on.