Mace Secret Room
To get to a secret room where you can obtain the mace, you have to get to the waterfall. Then you must make your way to the top. You will then see a big tree on the left side of a switch. Attack this tree with your sword and continue doing so until you connect with it. This causes a ball to shake free from within its branches. Pick up the ball and walk up the stairs. You'll find an open room. Drop the ball inside. You'll see the arches of several trees that reach into the higher level of the room. Go to the one in the middle and push on the side of it. When it turns, it will reveal a secret room hidden behind it where you can get the mace. With Yorda, take the ball into the room.
Mace Basket Ball
In the secret room, you have to use the ball you found to get the mace. First, you have to jump up onto the idol pedestal in the room. Yorda must jump with you. This will cause a basket to appear. Aim for the basket and throw the ball into it. This will cause the mace to come through the window in the room. You can get the ball into the basket another way, too. Before jumping onto the idol pedestal, put the ball in a square area that's on the ground. This is where the basket appears. Then when you jump onto the pedestal, the ball will fly up and automatically land in the basket.
Lightsaber
To get the lightsaber, you have to complete the entire game. Then you have to start a new one, then use all of the same actions that you took to get the mace. In this new game, you obtain a lightsaber instead -- which can quickly kill the Smoke creatures in the game. However, you cannot wield it alone. You have to hold Yorda's hand for it to work.
Extra Puzzle
You can find an extra puzzle in the game in the room leading to the top of the waterfall garden. The challenge is to get to the window. A switch is inside. Pull it down, and it will activate a huge piston inside the room. You can get to the window by standing on top of the piston. Once on top, jump just as it almost reaches its very lowest point. This launches you upward to a ledge. You can then climb up to the window and get out of the room.