Lord of the Rings Walkthrough:
Mines of Moria: The Evil Crystals of Doom
OK yes, I could have called this '21st Hall' or something. But every puzzle in this game up until now was reasonable if not a bit too easy. And then you get here. Giant crystals go up and down. Obviously it's a light puzzle, with lights going through the crystals. You even find a mirror, and there's a beam of incoming light. And then the frustration begins. Your light beam will NOT shoot at the crystals for some reason. The mirror doesn't do anything. The incoming light doesn't rebound to anywhere.
You fireblast everything in sight. Nothing works. So let me just tell you what I finally discovered out of sheer frustration and Rambo-like fury. You have to blast the INCOMING LIGHT 5 TIMES or so with your fireball spell so it turns into a "strong light". Does THAT make any sense to you?? You don't even use the mirror!!
OK so super-blast the incoming light. If somehow you have managed to get this far into the game without having read the manual and knowing how to TARGET things, this means that you press down on your right thumbstick, use your left thumbstick to aim at the incoming light spot, and press the button to SHOOT FIREBALLS at it a few times.
Now you have a strong light that is actually useful. The first door opens. Since the bit "exit" door is to the north, the door that opens is the southeast door. Kill the monsters in there and push the statue to the push-in spot on the floor. Lo and behold the next door opens, the one to the southwest. Kill those monsters and push the pillar out too.
Note that those annoying switches by each door is a 'crystal switch' - it turns the crystal left and right, opening/closing the pair of doors that are side by side. So use that to get into monster generators to the side of each door if you want to grab some extra goodies and/or up your monster kill count.
OK. Now slide out the pillar to the southwest for a moment (i.e. the second one) and now switch the switch to the northwest. It should allow the "real" northwest door to open, the one with the pillar behind it. Now put all 3 pillars on the spots and the final door should open. Push that final pillar in to the center and the master door will open up.
Note from littleidiot_1:
The point of the mirror in the 21st hall is so you can see easily where the beam of light is so that you can then use the proper crystal to bend it to where you need it to be.