Where do you get the green stick on Astro Knights Island?

The replacement for the glowing stick (a fuel rod) comes from the robot invader in the castle dungeon. If you get into his cell, he will self-destruct and you can take the rod.

To get the fuel rod :

1. Get the gold coin from the fountain.
2. Go to the Mordred Museum and get the library slip.
3. Go to the castle library and down into the dungeon.
4. Get the cheese and throw the switch.
5. Go to the Princess's room and get the mouse and Secret Message.
6. Go to the mill and get the passWord Cosmic Symbols from the loft girl.
7. Go to the fountain again, open the base (3 symbols and the Sun). Get the key to Mordred's lab.
8. Go to the field's hay bales and push them left and apart.
9. Open the lock on the secret laboartory
10. Feed the mouse to the robot owl.
11. Push through the wall into the tunnel.
12. Enter the cell. Merlin the owl will recover the fuel rod for you. (click on owl, click on rod)

(You will need to get the hoverboard to reach the saucer. See related question.)