After you find Leo's Paintbrush and learn Lisa's story, you can enter the World of Evil painting to rescue the Chief.
Explore the World of Evil
If you wish to exit the painting, you can just walk south from where you entered.
When you first enter the painting, you find two lairs of Dragon Birds. They fly in straight lines at a fixed distance, so just watch how they move and stay out of their way. Kill them to clear the lairs. The lair on the right will open the path, and the one on the left will release a tulip.
To the north, you find Stone Fire Pots. Unlike the Gepper torches in the Underground Castle, these torches are affiliated with a monster lair. They attack by shooting a fireball in a straight line in the direction where you are standing. They are easy to defeat. Clearing their lair will open the path.
You will find a couple of conveyor belts that both lead up to a monster lair. Spear Guys come out of this lair. They shoot spears in your direction after spinning around. Kill them and open the lair to open the path.
Go down the conveyor belt and go up the path that you opened. In the next area is another lair with Spear Guys. Clearing the lair will release a lonely goat. Go north to the next area.
There are a couple of Dragon Bird lairs here. The lair on the bottom will open the path, and the one at the top will release some ivy.
Continuing on, you will find a treasure chest. Inside is a Medical Herb. Unfortunately you can only carry one of any inventory object at a time, so this doesn't increase your number of Medical Herbs if you already have one. But if you have equipped your current Medical Herb, then opening the chest will heal all of your HP.
To the east you will find some blocks that hop around and have eyes. They are called Blocks of Doom. When you approach, the eye opens and it hops toward you. Kill the Blocks of Doom while avoiding the sharp spikes at the top and bottom of the room. When the lair is cleared, the path will open.
Beyond the three conveyor belts, you encounter a monster that your sword doesn't work on. It's a spinning, purple monster known as a Metagrinner. Your magic also doesn't affect this monster. Just avoid it for now until you have a weapon that can hurt it. Kill the Spear Guys coming out of the lair near the first Metagrinner. Open the lair to open the path, then go north through the new path.
There are more Metagrinners in the next area, as well as some Spear Guys. Kill the Spear Guys to release a goat in the house next to the warp tile that goes to the Grass Valley Shrine.
Go to the bottom-right corner of this room where there are more Blocks of Doom. Be careful to avoid the Metagrinners along the way. After you kill the Blocks of Doom, the lair will release a boy.
Go to the northeast corner of this room to find a Dragon Bird lair. Clear the lair to release a tulip.
Go northwest to the next room.
A conveyor belt will take you up to some Metagrinners and a lair that emits Spear Guys. Clearing their lair will create a warp tile to the left. This goes back to the Grass Valley shrine. If you go there, you'll be healed and can save the game, and you can return to Grass Valley if you wish.
Otherwise, continue going north. There are some Stone Fire Pots here. You can easily get rid of them all with one shot of the Flame Ball magic. Their lair releases a boy.
Keep going north, and kill the Spear Guys. Their lair opens the path. The dungeon boss is through the door that opened, and the room will lock after you go in. When you are ready, enter the boss room and you will fight the Metal Mantis.