Cheats for Castlevania: The Adventure for Game Boy

Locate the secret room in level 1 that contains a rope. Climb the rope to the top of the screen and through the ceiling. Collect the extra life, then find the extra life that appears later in the level. After both are collected, intentionally die and repeat this procedure.

Level 1
Locate the third set of rolling eyes. Climb the rope into the ceiling. 

Level 2
Locate the bridge. Continue moving downward until reaching a location where rolling eyes are falling to the right with stairs leading in the same direction. Destroy one of the eyes so it explodes on the second step from the bottom. Fall down the small hole that is created by the explosion. Climb down the invisible rope into the bonus room. 

Level 3
Just after escaping from the third set of spikes, a room where your character is in a narrow passage on the left with a solid wall to the right will appear. Climb the rope almost to the top, then jump off to the right and through the wall.

Level 4
Locate the room that seems empty except for a large figure that throws boomerangs. Climb the rope on the right about half way and jump off it, back to the middle. Your character should land on an invisible floor. Follow this floor to the center of the screen and climb an invisible rope through the ceiling.