You’ll first need to buy a ticket for her show at the Theater. After the show, she will hand over a banana peel with her autograph on it. This Signed Banana will give you access to the Fourside Sewers, as well as one of Ness’ Sanctuaries.
Detailed Walkthrough
After Poo permanently joins your party, you will currently be in Summers. Head over to the Museum and approach the guard. If you remember, Poo will have a Tiny Ruby in his inventory. Use this on the guard to appeal to his love of jewelry, and he’ll let you enter the hieroglyph room. You will be forced into a fight with two Shattered Man enemies. After the battle, examine the hieroglyphs and Poo will read them. He’ll eventually discover a secret code, and you’ll discover your next destination is the desert island of Scaraba. On your way out of the Museum, you’ll receive a phone call from someone called Mr. Spoon. He’ll tell you he’s found something amazing at the Museum in Fourside. When you arrive at Fourside, make your way over to the Museum. Approach the man on the left, and he’ll require an autograph from Topolla Theater’s new singer. So now you’ll want to head over to Topolla Theater, which is just across the street from the Museum. Once inside the Theater you can purchase a ticket and watch Venus’s performance. After the show, go backstage and talk to Venus. She will thank you by giving you a banana peel with her autograph on it. This is the Signed Banana!
What Does the Signed Banana Do?
If you return to the man in the Fourside Museum, you can give him the Signed Banana and he’ll let you through the door he’s guarding. On the other side is a room with a manhole. This is the entrance to the Fourside Sewers. You’ll need to be careful down here, as the enemies can be pretty tough. They will also disguise themselves as trash cans, and many of them can inflict poison. The Sewers are also home to some useful broken tools for Jeff, including the Broken Bazooka. When fixed, this becomes the supremely powerful Heavy Bazooka! If you follow the Sewers all the way to the right, you’ll eventually get to the entrance to Earthbound’s fifth Sanctuary, Magnet Hill. Before you can enter though, you’ll need to battle the Plague Rat of Doom. Don’t let this battle drag on for too long, as it’ll gradually become more deadly. Hit it with all you have and don’t be too scared to use your Bottle Rockets.