Continue game:
Wait for the title screen to re-appear after the game ends. Then, hold I + II + Down and press Run. You may now continue up to three times from the start of the last level played.

Super password:
Enter TORU as a name for one or both players to start game play at the cave past the first Boss with an experience level of 20.

Enter AGAG as a name to start the game halfway through the fourth continent (the subterranean area with all the skulls) at level 20. This only places you at this location; if you go backwards in the game from here, you will not have most of the unique items (for example, the Scale Of The Mermaid) except for the Silver Key.
Information in this section was contributed by Dave Perry.

Hint: Secret items in final castle:
In the final castle, there are two areas with secret items. After the first few staircases and doors, in the outside area which contains an herb, there are hidden ropes that you can reach from the stairs. Jump across these ropes to find a Life Bell. There is also a secret area reachable from the long rope right after finding the Princess. Jump into the empty space at the bottom of the rope (not from the ground, but from the rope itself). There is a Life Bell and an Elixir in this area. Although not very obvious, the room with the Blue Dragons in the early part of the castle leads to an outside area where there is another Elixir.
Information in this section was contributed by Dave Perry.

Amulet of Dragon special item:
Locate the rope and rock on continent four. Jump from the rope and walk through rock to find the Amulet of Dragon to receive 65,535 gold. Note: A green dragon is located on the ledge to the top left of the rope.