Play until reaching a situation where a slow moving monster, like a jelly, is above your character in a lengthy vertical hall. Move down until the monster is almost off the top of the screen, then quickly move back up. If the timing was correct, the monster at the top of the screen will have been duplicated and there will be two of them.

While playing the game, press 1 and 9 at the same time to pause the game.

If you immediately head to the bottom right corner of the main map, you can push buttons at random and down+right to reappear in the top left corner. This gives you a straight walk to the final cave, no canoe needed.