:: Silver Key

The first key you need to get is silver. You can find it in the chamber near the entrance to the blue castle (pictured). Just keep going right. On the other side of the door is an Armored Pig who holds the key.

:: Gold Key

Once you've picked up the silver key, you can find the silver door up to the left. It's just above the entrance and quite easy to miss. There's a gold key flying around outside. If you have trouble reaching it, you can also shoot it down.

:: Globes

1. Jump through the wall to the left at the very start. After you pick up the bronze key, run left and jump down the large gap. Keep moving left -- there's a globe halfway down. Now run right and jump up a couple of ledges with the blue flower. On the right, you'll see two blocks with circles on them. You can shoot through these and run through.

:: Very Secret Place

Between the two bronze doors at the top of the castle there is a hidden passage at the corner of the corridor. Jump left out onto the roof. If you then leap off to the left with the help of the blue flower, you'll land on an invisible platform. Follow your nose until you fall back down again, and then run right without jumping up to find a chamber which has a purple dragon inside.

:: Yellow Wizards

Try and pick off the other wizards first.. it's very difficult trying to deal with both heat-seeking orbs and fireworks at the same time. When each blast showers down, concentrate on finding a gap to stand in before you resume shooting at the wizard. You can also take down the yellow wizard with a series of hit and run attacks, but it takes a long time!