The naked lady level?
When you are creating the saccharine cuteness of the Kirby world, it must be hard not to slip in some inappropriate content. This was especially true in the old days of Nintendo when they were super strict on what was allowed into their games. During the SNES era, you weren't allowed to use the word "Pub" on a building, due to the implications of possible alcohol use. The tiny sprite of a dancer in a bathing suit was considered too raunchy for Final Fantasy IV (known as II in America). This meant that if you wanted to include something rude into a Nintendo game, then you had to get creative.

It seems that the creators of Kirby's Dream Land 2 wanted to include some lewdness into the game. They managed to do this in a very subtle way. If you can find the secret stage in level 5-5, then you will find an arrangement of blocks that resemble a very basic outline of a naked lady.