William's Zweihander is an immense sword. While part of Team Lyoko, William used it mostly for swinging, using its huge size to his advantage by swinging it like a bat, causing him to slide across the ground and to spin around several times, hacking monsters along the way. This could be due to his inexperience with the weapon, as it appears to have been created mainly to send silver waves of energy flying at his enemies. Glowing white energy slowly climbs up the blade from the hilt, and when it reaches the blade's tip, a single wave of the sword releases the energy into a silver slicing wake, dealing heavy damage - supposedly by the will of whomever is holding it.
After being possessed by X.A.N.A., William's Zweihander gets a few modifications. It seems easier to handle, making actual sword-fight possible with the weapon. The white energy doesn't need to climb the blade, the whole blade glows automatically, and while the waves still take time to execute, using them is much quicker than before. Incorporated into his Super Smoke ability, if William and his Zweihander are separated, the sword can transform into dark-colored smoke and return to his hand. On both sides of the hilt, a white bulge with an Eye of X.A.N.A. is present. If another's energy, like Aelita's Energy Fields, hits this bulge, it will be absorbed by the sword, making it's energy waves even more powerful.
The Zweihander, when used by William as part of Team Lyoko, looks similar to a butcher knife. It has a slender, red handle and a dark grey triangular hilt with an image on the back of his ID card on it as decoration. The blade has a camouflage-like design on it with two chips in it near the tip. The blade glows white whenever it comes in to contact with anything.
While under X.A.N.A.'s control, the Zweihander changes in appearance. While still the same shape and size, the Zweihander's handle changes to an ebony color, red at the end. The triangular hilt is replaced with dark grey root-like structures reaching about a third of the way up the blade, with the Eye of X.A.N.A. at the hilt as well. The actual blade loses its camouflage design and is now a grey color. The blade still glows white on contact.
In Code Lyoko Evolution, the sword changes to a more jagged and rusty appearance. The handle becomes black with a red spiral pattern down it and the hilt is completely gone. The blade is a metallic grey metal colour with lighter grey near the blade edge and dark grey near the other. It also appears to be smaller in Evolution. It is decorated with rusty red lines coming from the handle and the blade edge has a jagged, almost serrated, look.
- The "zwei" in Zweihander is German for the number two, hinting at a possible meaning for the name to be "two-hander". This would make sense since the weapon's weight means the user has to hold it with two hands to make combat possible.
- The Zweihander was the weapon that destroyed the Core of Lyoko in Final Round.
- The Zweihander has the ability to absorb Aelita's Energy Field, and redirect it.
- The vines on the Zweihander are black on Lyoko, but are red in the real world.