Red Balls of Fury was a rather pain-inducing firebending move invented by Fire Lord Mario during his reign over the Fire Nation. The move involved a fireball of intense heat being launched from the palm of the hand of the user. To make the move more effective, the fireball was usually fired at the victim's sensitive area. Red Balls of Fury could only be achieved by high level firebenders since it involved the creation of an intensely hot fireball in a fraction of a second. As soon as the fireball was created, it would immediately be shot outward toward the victim.
This attack was the signature move of Fire Lord Mario and it was a move that was commonly performed by Iroh.