Find and Enter the Midoro Palace
First make your way back to the swamp area and continue through until you've reached the Midoro Palace. Once you have entered the palace take the first elevator all the way down. Continue right until you have reached a key at the end, grab it and head back to the elevator. Now take it up one level and continue to the left. Walk to the end to find the second key, grab it and head back. Take the elevator up another level and go left. Defeat enemies and unlock the door in your path. You will reach a fire pit with a key sitting on a platform, jump to it and grab it, continue left.
Keep walking left until you've reached the second elevator. Take it down one level and go left again and unlock the door in the way. Avoid the falling blocks and continue going left. You will soon reach another locked door holding the palace's treasure. Defeat the enemy and unlock the door to obtain the handy glove. Head back to the second elevator and take it all the way down. You can now destroy the bricks blocking your path, do so and continue walking right. You will see the third elevator, ignore it for now and keep going right to find another key at the end. Grab the key and go to the third elevator and take it down.
Continue to the right and you will see another small lava pit, you can ignore it or try and grab the point bag. Continue right and unlock the door in front of you to confront the palace boss, Helmethead.
Palace Boss : Helmethead
To defeat Helmethead, the easiest strategy is to to jump over him and use the downward thrust to take out his helmet. It will soon break off and float around the room shooting fireballs at you. While avoiding the fireballs, continue to strike him and he will eventually be defeated. Once he is destroyed, grab the key that falls and unlock the door to place the second crystal.