To buy Superhuman in Blox Fruits, follow these steps closely. First, ensure you have access to the 2nd or 3rd sea. You will need 3 million Beli and 300 Mastery on four specific fighting styles: Electric, Water Kung Fu, Dragon Breath, and Dark Step.
Next, obtain the required fighting styles. Electric, Water Kung Fu, and Dark Step are available at the Half Cold Half Ice Island. You can purchase Dragon Breath for 1500 fragments at a specific location, like the Cafe inside the bridge.
Now, focus on farming Mastery. You need to reach 300 Mastery on each of the four fighting styles. This can be achieved by farming NPCs and bosses.
Once you have all the requirements, head to the Snow Mountain to find the Martial Arts Master. Cross the bridge and enter a small entrance to locate the Master. If you meet all the conditions, you can buy Superhuman for 3 million Beli.
For easier progress, consider using a private server. Buddha can help with Beli farming, and the Double Mastery game pass can speed up the process.