You will get this while playing the game. This is the boss fight at the end of the Sky world.
How to defeat this boss: You can damage him by jumping on his head, shooting him and using specials from enemies. This makes this even easier than the first time you encounter a boss. Jumping on his head does the most damage and is only 4-5 hits like the previous boss. Once he is hit he will fly up and cannons on the side of the map will shoot enemies at you these will come in 3's and are completely random. If you get the orange monster he will usually drop a bomb once he dies which you can then pick up and use the clouds to get high enough and activate the bomb which damages the boss a lot this is why it is a lot easier to complete than the original boss. He does not change attacks at all and his only attack is to hover right to left or vice versa when he lowers to ground level and uses saw blades so it gives you a good chance to jump on his head. Repeating this 3 - 4 times will give you this achievement.