After getting the Staff of Fennel, you need to speak to Prometheus to get the power of fire.
Go to Argolis
After you get the Staff of Fennel, leave the woman's house and go to the right until you find some stairs leading up to the next screen. From here, go up the two sets of stairs to go to the next screen. Then go to the left until you see a door in the rock wall. Press up to go through it. You will return to Arcadia.
You might want to go to Zeus's temple to get a password so that you will restart in Arcadia if you get a game over and choose Retry. The white house that leads to Zeus's temple is one screen to the right of the house that leads to Attica. After you leave Zeus's temple, follow the path until you're in front of the white house in the forest, then go to the left to return to the screen with the house that leads to Attica.
Go to the left and you will pass by some trees that have doors in them. Ignore the first two doors, and go into the third tree door (it's the last one before the end of the forest). You will find an old woman, and there is a door to the right of her. Go through that door and you will be in a new area of the forest.
Go to the left and there will be another small creature who will throw spears at you. There are also more slimes that will fall from above. Make your way to the left. You can ignore the two-story building. Go to the left from there to find a small house. Go inside and you will be in Argolis.
Visit Hermes's Temple
Go to the far right of this area to find two doors side-by-side. Go into the door on the right.
Inside the cave, you will encounter snakes and bats. The snakes will slither toward you, then when they get close, they will jump toward you. The bats are hiding on the ceiling, and when you get close, they will swoop down toward you. All you can do is run away and try to hit them when they are at your level.
From the beginning of the cave, go right and jump over the pit. Then go to the right, ignoring the two doors that you pass. Jump over the next two pits and go to the right to reach the next area.
Ignore the door, then go to the right and jump over the two pits. Go into the door here to find Hermes's temple. Talk to the man at the end, who says that Hermes was summoned by Zeus. This means that you will have to go to Zeus's temple to talk to Hermes.
Optional: Get Ambrosia and Salamander Skins
Before you do that, you can get some optional items. The Ambrosia increases your maximum health, and Salamander Skins will allow you to get a more powerful shield later. However, the Salamanders that you have to fight are very powerful, so you might want to come back here later when you are stronger.
To reach the Salamanders' Nest, leave Hermes's temple and fall into the pit to the left of his temple door. This takes you to the Salamanders' Nest. These snakes are very strong and will hurt you a lot if they touch you. But you need to kill them until you have 50 olives and 20 Salamander Skins (check the START screen to see how many skins you have).
The key to defeating the Salamanders is to rush toward them, kneel and hit them before they can jump. If you're lucky, they will jump over you if you miss. Also, when a new salamander falls from the ceiling, it jumps forward a little bit before landing on the ground, so keep this in mind if you want to attack a salamander that is falling from the ceiling.
If you are having too much trouble against the salamanders, go to the far right of the Salamanders' Nest and go through the door, then go back to the Salamanders' Nest. Go to the left and jump up two of the three steps to make the Salamander jump toward you. Hit it when it gets close (no need to kneel while standing on the lower step), then go through the door to escape. Then just go through the door that you came out of to return to the Salamanders' Nest, and repeat the process until you have 20 Salamander Skins and 50 olives.
When you have 50 olives, go into the door in the middle of the Salamanders' Nest and talk to the old woman there to buy Ambrosia. This increases your maximum health.
If you went down into the Salamanders' Nest, go through the far-right door, then go to the left and go through the door to return to the first area of Argolis.
If you did not go to the Salamanders' Nest but did go to Hermes's temple, then leave Hermes's temple and go left until you reach the next screen.
You can optionally go to a nectar fountain that is hidden here. Just fall into the first pit, then go to the right, fighting the snakes (they are normal, weaker snakes, not salamanders), and go into the middle door to find the fountain. From there, exit the room with the fountain and go to the right, then go through the door at the end, and finally go through the left door to return to the first area of Argolis.
If you decided to skip the fountain that was mentioned in the previous paragraph, then just go left until you reach a dead end. Go through the door to return to the first area of Argolis.
Then go into the door to the left of the one that you just came out of. You will be in a different cave. Go to the right and ignore the door, then jump over the pit and go to the right to reach the next area.
Go to the right and jump over the three pits. There is a lion to the right that you will need to fight. Slowly go to the right to get rid of the bats. Then approach the lion while swinging the Staff of Fennel. When you walk in front of the black part of the background that is to the left of the lion, the lion will suddenly run toward you, so you will need to rapidly swing the staff in order to hit it before it hits you. Keep swinging the staff because the lion will keep running toward you after you hit it.
After you hit it three times with the staff, it dies, and a door appears. Go through the door and talk to Prometheus, who adds the power of fire to the staff. To use it, press up, then the attack button, while the Staff of Fennel is equipped. A flame will shoot out of the staff. You can't shoot another flame until the first one disappears.
If you have the power of fire and you visited Hermes's temple, you should go back to Arcadia and visit Zeus's temple, where you can talk to Hermes.