Save your position in the dungeons or caves. The go through it and open doors until you run out of keys. Now restore your position, and you will have all your keys, but all the doors will still be open. Repeat as often as you need.
Go to the dark evil castle. Stand right up against the force field. Let yourself starve so that you faint. When you wake up, you'll be on the other side of the forcefield.
Find the green turtle, jump on his back and start attacking. Nothing will happen except your bravery points will keep piling up.
On the island with the Crystal Castle press RIGHT MOUSE BUTTON while speaking with the sorceress and luck increases to 65. Ask the sorceress several times.
A secret entrance to the fort exists. On the left side, near even with the door.
If running low on Green keys, use a secret entrance for the fort. It's on the left side, almost even with the door.
Beating the Turtle is not beating, it is pushing, so push the turtle across the land, to use it in special places: The turtle was programmed in asbestos, and can swim in Lava. It can be used to enter the black citadel at the south. Also, while it is present, you are not attacked, but by the time one has the turtle, one is already invincible.
Save a game to a back up file and patch byte 18 to a non-zero value and you know have these cheats at your disposal:
ARROW KEYS--Move very fast over any terrain
'B'------------------------Summon gold swan
'R'-------------------------Rescue princess
'='---------------------Display coordinates
'F9'--------------Increase time by one hour
'F10'---------------Location in coordinates