In Pokemon Blue where do you get a pokeflute?

In Pokemon Blue, Mr. Fugi gives you a pokeflute when you rescue him from Team Rocket in the Pokemon Tower (which is in Lavender Town). In order to get to him though, you need a Silph Scope so that you can fight the level 30 ghost Marowak that blocks the way.

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First, you need to go to the game corner. In the back, there is a poster that has a button behind it. Push it and a secret door opens the team rocket hide out. Once you get to the end you have to fight Giovanni and then he leaves behind the silph scope. You use this to reveal that the ghost in the Pokemon tower was just a Marowak. Fight it and get up the stairs. There will be a few rocket grunts wanting to fight. Then at the end is Mr.Fuji who is so grateful for you saving him he gives you the pokeflute.