Big Duo first appears in episode 12 as the first other "Big" that Roger encounters as well as the first robot that is able to fly. It is piloted by Schwarzwald, who attempts to use his Megadeus to make people aware of the truth of forty years ago. After a brief confrontation at the beginning of the episode, Big O and Big Duo meet again in battle in the central dome towards the end. Big Duo is defeated when Big O drops from the top of the dome in a surprise attack and removes one of Big Duo's arms. In an attempt to permanently disable the Megadeus, Big O then crushes Big Duo's head with its arm pistons and tears off its front chest plate. After being defeated, Roger and Schwarzwald watch in amazement as the damaged Big Duo acts on its own to crawl toward Paradigm Headquarters and reach toward the central building before finally collapsing. In episodes 13 and 17, however, there is evidence that Big Duo is being rebuilt...
Big Duo first appears wrapped in bandages, much like its pilot. This disguise doubles as an attack which uses the bandages to temporarily immobilize the opponent.
Identical to Big O's eye lasers, this technique is useful as a long range attack and for cutting through objects.
Schwarzwald uses this wall of smoke to make a stealthy and dramatic escape.
Big Duo's most distunguishing feature is its ability to fly. It accomplishes this by spinning its fingers into propellers while the rocket boosters in its arms support it from behind. Schwarzwald makes use of the maneuverability of flight for quick movements and strategic attacks.
Big Duo can rapidly fire alternating missiles from panels in its chest area. This attack is useful from a distance or to attack an enemy on the ground while in flight.
Likely its most powerful weapon, Big Duo's megaton missiles are located in its lower leg panels and are shot from its knee area. While very destructive weapons, a drawback is that these missiles can only be fired one time before needing to be replenished.