Shadowgate 64:Trials of the Four Towers
How to find the Rusty Key
Go to the room where you find a note to the custodian asking for another key to the underground tunnel. There will be a key between the column and wall. This key is very important.
 Find The Rusty Key
 Cheat in Tower 3
 Get Into The Control
 Room
 Defeat the Warlock
 Lord & Belezar
Cheat in Trial Tower 3
When you gain access to the Inner Chamber (Tower #2), take all three rings, red, blue, and green. When you get to the 4th trial, (maze that mixes up the controls), equip the blue ring and your controls will return to normal and you can proceed through the maze like you were playing an ordinary area. Once you step through the door at the end, remove the blue ring.

How to get into the Control Room
To get into the control room you must first get the Stone of Thirst from Dorn. Then go to the grave on the side of the Chapel door, the one blocked by wood that you can pull away. Use the Ring of the Dead to speak to the soul and then throw some Dragon's Tears on the grave. Speak to him again. He will tell you the Stone's incantation. Go to the resevoir (tunnels in excavation area 2) and use the Stone in the water. Climb down the ladder and up the ladder on the other side of the room. You are now in the Control Room!

Defeat the Warlock Lord & Belezar
To defeat Belezar, put the dragon eye on the fake Staff Of Ages. Then, to defeat the Warlock Lord, put the Staff of Ages and the ring in the hands of the statue of Lord Jair.( Note: put the Staff of Ages on the statue FIRST and always wear the Ring of the Kingdom when handling the Staff of Ages.) After that, you will have beaten the game!
Credit Goes To:Paul A Larson via IGN 64