Adventure Time: Hey Ice King! Why'd You Steal Our Garbage?! (Nintendo 3DS)
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New Game+
Beat the game once to unlock NG+, and to access it, hit the arrow next to the plus symbol on the file select screen.
Secret Screen
To view a hidden screen press Up, Up, Down, Down, Left, Right, Left, Right, B, A at the 'Title' screen.
Song Listen
In order to unlock this "Song Listen" you have to beat the New Game+.