Gus is an enemy from Paper Mario 2. He is an optional enemy in the game. He can be fought in Rogueport. Gus works for the crooked side of town known as the Robos. Gus also has a relative but is not fought.
If Mario decides to fight him rather than paying 10 coins, he can fight Gus. Gus is particularly weak but for the first chapter, he can seem powerful. Taking Gus early on is not recommended but can be done. The best way to do this is by superguarding the attacks or through a defense badge.