He was created by Negative Mario, and is a helper to continue his legacy just in case. He is not actually his brother, rather his son. He told him in his mind to kill Mario. He first punched away AGK and Stanley Jones, as he came out of a Portal. Mario was shocked right away and used a Hammer. It did nothing. Doomguy shot a bullet, it also did nothing. He used a war scream to scare Mario. AGK became a giant thanks to the Mega Mushroom, and tried to crush him. It still failed, so he used a Bomb Keyboard. You guessed it! It still failed. He was defeated by Inferno Mario with a Hammer.
This power is only owned by him. It can bounce, and when touched, it shocks/electrocutes you. It was used on Doomguy, Shrek, and Mario. AGK was able to dodge this, but then it grew in size. Still, a Bomb Keyboard took it away.