Wario Land 4

In the final boss, depending on how many treasure chests you have after beating it alters the appearence of what the princess looks like during the ending. Here's a list of what different appearences you can get & how many treasure chests you'll need.

Here are some tricks to enjoy the secret feature even more:
*press up or down to raise or lower the pitch.
*press left or right to change the tempo.
*press L or R to change the CD from green to yellow and only the lyrics.

To get Wario Karaoke (Listening to songs from the game, with Lyrics.), get gold crowns in every level.

To get a gold crown, you need to get 10,000 coins in a level.
To get a silver crown, you need to get about 8,000 coins.
To get a bronze crown, you need to get about 6,000 coins.
To get no crown, get less then about 6,000 coins.