To defeat the big guys, shoot them in the face with an arrow to stun them. slash away and get him down on his knees. piggyback ride him off the cliffs. do this with 3 of them and you can proceed.
In the underground you'll have to fight off a large amount of enemies activate all the crystals on the walls with your magic and proceed through the big door.
Fight a few more enemies and make your way up the spiral stairs. ( I advice just to run past all the enemies on the stairs as you will hit a checkpoint at the top there and they will dissappear )
When fighting on the big diamond floor don't piggyback ride on the enemies just shoot them in the face with arrows and slash away.
The puzzle in the next room is: Red Green Yellow Red Green.
This last stage is rather annoying. you'll have to fight 2 big ones and after that you can proceed ( 4 enemies will come breaking through a wall ) you'll have to call in your dragon to destroy the tower and fight of more enemies. Once again enemies will come through a wall on your right. now when you climb up that wall break the chest to replenish your health and just run past all the enemies as there are way to many to beat them all.
That should be another 30 G :)