The Key of Stones

You land into an area with three snakes and a lizard. Before continuing, grab the Twin Snakes fragment from the pot that is hidden near you.

Now go forward until the lizard sees you. Go to the left and continue on to the end and kill the middle snake. Kill the snake that is now to the left. Don't go towards the wall since it is within range of the remaining snake. But just turn around the corner, seemingly chasing after the lizard.

Make your way around till you can kill the snake from its side. Head down the wall and do the usual thing with lizards and cracks. He will fall. No matter which side he falls on, he will be vulnerable so head over to his position to kill him from the side. Flip the lever when you are done and go on top of the gray platform to see a pot that contains an emerald. Go to the next area.

Grab the emerald from the pot immediately after you arrive. It is located in an alcove just in front of you.

Move forward to show yourself to the lizard. Kill this lizard by going left towards the crack and making him fall into the abyss. Now go back and trigger the remaining crack. Then go down and show yourself to the lizard to get him out of the way. Head back to the crack to fall down and head to the chamber which houses the Key of Stones. You will do the same thing with the other keys. Insert it at the gate and head to the next area that opens.