The Mysterious Warrior (謎の格闘家 Nazo no Kakutōka , lit. "The Mysterious Martial Artist") is the final boss in the Famicom/NES version of Double Dragon II: The Revenge, who replaces Willy as the game's main antagonist in those versions.
The Mysterious Warrior's true name and origin are unknown. All that is known about him is that he is the successor of a deadly martial art known as Gen-Setsu-Ken (幻殺拳, lit. "Phantom Murder Fist"), whose school has been in conflict with the Lee brothers' own style of Sou-Setsu-Ken (双截拳) for generations due to their opposing ideals. He forms his own organization following the downfall of the Black Warriors, targeting various martial artists, including the students of the Lee brothers' own school. When Billy Lee's girlfriend, Marian, is killed during one of their attacks, the Lee brothers pursue the organization until reaching their island stronghold, eventually coming face to face with the leader himself. After being defeated by the Lee brothers, the Warrior tells them about a prophecy that has been passed down within his school. After his death, the Lee brothers return to their home only to find that Marian has been miraculously brought back to life.
In the Famicom version of Double Dragon II, the Warrior always appears regardless of the difficulty the game is set on, whereas in the NES version he only appears on the hardest setting ("Supreme Master"). The battle against him consists of two phases. During the first phase, he fights on a green field at night with a demonic statue and a pair of eyes in the background. After he takes sufficient damage, the background changes to the interior of a temple. His techniques include a thrust, a roundhouse kick, a backflip kick and a spinning clothesline. He can also turn invisible at will during the first phase. After the Warrior is defeated, Marian will return to life.
In the PC Engine version, the Warrior can be fought on any of the three different difficulty settings, although the ending differs depending on the choice. On the easiest setting, the Warrior will escape after the first phase of the battle, mocking the Lee brothers for their failure to defeat him, resulting in the bad ending.
- While his organization is never given a name in the Japanese version, the English localization refers to them as the "Black Shadow Warriors" in the manual and "Shadow Warriors" in the opening sequence. The only other time the term "Shadow Warrior" appears in the English script is when the player character uses it to address the Mysterious Warrior himself prior to their final confrontation. "Shadow Warriors" would be used as the name of the enemy organization in later games and works, such as Super Double Dragon, Double Dragon V: The Shadow Falls, the animated series and Double Dragon Advance.
- The Mysterious Warrior is alternatively known as the "Supreme Black Shadow Sensei" in the English manual of Double Dragon III: The Sacred Stones.
- In Double Dragon Advance, a group of enemy characters modeled after the Mysterious Warrior appear as an elite enemy group that serve as Willy's bodyguards. They are known as the "Five Emperors" and are successors of a martial art known as Gen-Setsu-Ken (幻截拳), appearing as the end bosses of the penultimate stage. When the player confronts Raymond, the head of the group, the standard boss theme is replaced by the Mysterious Warrior's theme from the NES version of Double Dragon II: The Revenge, "Fight of Fate".