Watch a short video walkthrough of this stage.
First you have to get off the Eagle. Immediately drop down onto the stone bridge. Two Skeletons will appear on the eagle. Wait for them to drop down then ram them off the bridge if you can.
Head to the right and jump-attack the Lemanaya to get her off the dragon, then use it against her. Next up you'll meet a Red Longmoan and Red Heninger. Treat them as usual. Next you'll face another Red Longmoan and two more Red Heningers. Up next are the bosses.
Two Colonel Bitters will march up. Use your magic to weaken them if you wish. Since they can't run you can quite easily separate them and then stand between them and alternately dash-attack each. Up next is the castle.
Again, if you are playing the arcade, the knights are much more difficult opponents, and you should kill them with the dragon if you still have it. The flame range on the dragon is greater then their attack range, so you will win easily, and you can exploit the enemies lack of mercy invincibility by greeting them with fire as they stand up.