The Master Ball is a type of Pokéball that has a 100% catch rate on any Pokémon that is capable of being captured. As it is an incredibly powerful item, it appears throughout the game in extremely limited quantities.
Team Asgard/Olympus BaseEdit
To obtain the Master Ball in the opposing team's base, there will be a computer on the 1st floor that has a program called "masterball.exe". Run it and find the previously empty room to obtain a Master Ball.
The player can obtain a Master Ball from the Pokéball in their Secret Base. It has one of lowest chances to spawn (~1%), but it is still obtainable with enough patience.
The best Ball with the ultimate level of performance. It will catch any wild Pokémon without fail.