The Galley Oar is Nightmare's joke weapon in Soulcalibur II and Siegfried's joke weapon in Soulcalibur III. It can be seen in the intro as Nightmare fights Mitsurugi. The swordsman referenced in the description is Miyamoto Musashi, who carved a sword from an oar for use in his duel with Sasaki Kojiro, and killed him with a single blow with the weapon.
"A warrior from the east used something like this, apparently."
— Weapon Gallery description.
"An oar from a galley ship with its handle cut short to make it easier to carry around. Perhaps it was modified by someone who heard the legend of the Japanese swordsman who won a duel with an oar and decided to try it himself. The ridiculous sight of using it as a weapon might cause opponents to let down their guard."