Any Sea of Thieves pirate looking to complete the Three Trials will need several items, namely a Mighty Pirate Sword and a Rubber Chicken. But first, we needed to find them.
Where to get the Mighty Pirate Sword and Rubber Chicken in The Quest for Guybrush - Sea of Thieves
You can find the Mighty Pirate Sword and Rubber Chicken in the Mêlée Island General Store. However, they both have expensive price tags, and you can't find any Pieces o' Eight to buy them. Instead, speak to the Shopkeeper about taking a line of credit.
Surprisingly, he is willing to do so, but you must get a Credit Note signed by Governor Guybrush.
How to get Guybrush’s Signed Credit Note in The Quest for Guybrush - Sea of Thieves
The Shopkeeper hands you a blank Credit Note and tells you to return it with it signed by the Governor. Head up to the Mêlée Island Mansion. You'll see Guybrush is asleep, meaning you must forge his signature. To do this, you must get the Captain's Inkwell and a quill.
Place both items on Guybrush's desk, and you can forge his signature. Return to the Shopkeeper and hand him the Signed Credit Note. You can now purchase the Mighty Pirate Sword, located to the left of the Shopkeeper, and the Rubber Chicken, located on the top floor. Both items are needed to complete the Three Trials, along with the Treasure Map.
Where to find the Captain’s Inkwell and Writing Quill in The Quest for Guybrush - Sea of Thieves
The Captain's Inkwell is located in the locked storage chest in Guybrush's office. Pickpocket the key from the sleeping Guybrush and use this to open the chest. Place the Captain's Inkwell on the desk and head downstairs.
Writing Quill Location
The quill is found on the table to the right of the main doorway. Simply swipe it from the table and place it on Guybrush's desk.