Defeating the guardians is not that tough, it is just a little difficult to explain. But I will try nevertheless: If you jump on a platform, the platforms around your platform will arise or sink. Now you have to make the platforms the guardians are on sink. It will only take some attempts. The main problem is that the guardians are moving as well.
Pick up the hero's stone. Now you have to run. This passage is another example of great level design. Quite difficult jump-and-run-passages, much action, variety. Well, I like this whole level very much.
Despite of the ground shaking, take your time when you cross the first room. The path you are walking on is not too broad. Carefully navigate through this room and you should be safe. Then you will experience one of the nicest passages, enjoy it. If you get through it you will break into the room where you jumped from blocks to blocks.
Now return to the very first room of the level. This time, turn right and take the stairway made of big rocks up. This room works the same way as the ventilation shafts in the Overlord's castle. At the very top you will leave it. Jump over the gap and you will soon be back on Hero's Island. Make your way back to the main island.
Since I don't want to pick up FEATHERS again go to the house of the Elder. I know, you can't enter it right now. But left of it you will find a path leading to the aqueduct. Look around and after a while you will find it.
Cross the aqueduct. Make sure to avoid mines and water leaks which is not really difficult.
Once you are on the other side take the lift down. You have to reach the cage-looking elevator. The path to this elevator is full of mines so take care. If you are low on health look around. There are several barrels with hearts in them.
Step into the elevator.
This is the warming - up. Pick up one of the shooting items (in the barrels you will find more and better ones of these) and shoot all the enemies. Since some of your opponents are loosing hearts once they die you should not run out of health.
More enemies, more fun! That's all.
This is the interesting round. Your main targets are the big monsters. But they are invincible by now. What to do? Fill up your shield energy and use one of the three elevators in the arena. You will be taken to a shield generator. Use it and once you are in a big shield ram one of the huge monsters. It will burn for a short while and it will loose its shield forever! Now pick up a shooting item and shoot at the monster until it dies (if you did everything right it will burn after every hit). Now load up your shield energy again and go for the roof of the area again. You have to take out the other two enemies the same way. Once they are dead simply shoot the last few machines and you will get the Hero's Stone.
Leave the arena.
Leave the cave (there is a natural stairway, you will see it easily, there is an antidote on each of the stairs). Cross the aqueduct again (to get the ride, jump and press attack button).
Your next job is to go for the blue FEATHERS. So turn left. You will see a big shining round field eventually. A little to the right of this position you will be able to jump on the hills. Turn left and you will find the first FEATHER in a barrel above. Use the platforms to the left to reach a platform with several barrels. One of these contains a shooting item. Shoot all the mines in this area (believe me, you will thank me for this advice).