whenever i fight him its always shows "0" in the green orb...
do i need to keep fighting yill ill see an orb?
As said, it has a drop chance. It's quest item. So you need to farm dark lord for a green gem drop. (You need 9 to be able to finish the full world) Just keep fighting
ah this part was confusing for me also. It isn't explained very well.
So is there anything I can be doing with my full energy bar while I'm failing at getting the drop needed to continue?
Not really. Energy can currently only be used to progress further into the story. So basically, you're stuck with a full energy bar until you can continue.