William generally fights by using the Zweihänder's size it his advantage.
In Final Round, William primarily uses the Zweihänder to deliver slow but powerful blows, defeating Creepers with a single hit. For defense, William is able to reflect lasers by at monsters using the sword. After being possessed by X.A.N.A., the Zweihänder gains the ability to charge and then release energy in the form of silver waves, which are also rather slow to execute, but exceptionally powerful.
After William's return in season three, the Zweihänder receives several upgrades from X.A.N.A. With William's increased physical strength, the sword is easier to handle, increasing his dexterity with the weapon. The Zweihänder is also heavily integrated with William's Super Smoke ability, and he is able to use the ability to make the sword vanish when not using it, or summon it directly to him if he is separated from it.
The Zweihänder is a massive sword, longer than William is tall. It has a wide, single-edged blade and a long, thin handle. The blade is silver in color and glows white when being used in combat, including while charging a wave attack. Apart from these general features, the Zweihänder goes through several appearance changes throughout the series.
While William is under X.A.N.A.'s control, the Zweihänder's handle changes from red to black, and black, root-like structures decorate the blade. There is also an Eye of X.A.N.A. near the sword's hilt. While on Earth as a spectre, the Zweihänder blade is a darker shape of grey, and the roots on the blade are red instead of black.
In Code Lyoko Evolution, the Zweihänder's appearance changes again. The handle is black with orange stripes, and there is an orange, circuit-like design on the blade. The sword is also noticeably smaller than it is in the original series.
- A Zweihänder is a traditional German sword used primarily during the early 16th century. The name translates into English as "two-hander", and like William's weapon, real-world Zweihänders are known for their exceptional size, and must be handled with both hands.
- The Zweihänder's design appears to be based on the Buster Sword from the Final Fantasy series.
- The Zweihänder was the weapon that destroyed the Core of Lyoko in the season three finale.
- If one of Aelita's Energy Fields hits the Eye of X.A.N.A. on the Zweihänder, its blade will glow pink instead of white, and William will be able to redirect the attack in the form of a wave.