Impostor Captain Tennille

The Captain Tennille imposter is an enemy stand user of Part III: Stardust Crusaders.

Appearance/Personality
The imposter appears as a tall, muscular man possibly in his late thirties. Though the reader is never shown the true Captain Tennile, one can assume that he was practically identical to the imposter, since his men, who had worked for ten years on the same ship, did not even suspect the replacement.

The imposter appears to be very patient, as he originally planned to separate the protagonists and kill them one by one. Once his schemes are spoiled by Jotaro, he does not lose his calm, saying that it will be no problem for him to kill them all at once from underwater. He also enjoyed to guess what his enemies where thinking.

He also seems to be fond of the ocean, being rude towards Jotaro after seeing he was smoking and asking if he was going to throw the ashes and the cigar in the water.

History
The imposter is one of the Tarot Card representants sent by Enya Gail to kill the Joestar group. Seeing that the Joestar group decided to travel by sea after the attack of Gray Fly and how the Captain of the ship looks just like him, he decides to kill the captain and take his place. He throws the captain into the ocean and boards the ship with everyone else, no one noticing that he isn't the real Tennille. He plans to kill the group one by one while inside the ship.

Stardust Crusaders
The imposter appears on a boat that Jotaro Kujo and company have taken to go from Hong Kong to Singapore. After Jotaro and Runaway Girl are attacked in the water by a mysterious creature, Jotaro has become suspicious of the crew members and believes one of them may be a Stand user.

Although Joseph Joestar insists that the Speedwagon Foundation had checked his credentials, Jotaro decides to find out if he is the culprit anyway by playing a bluff on him: he says that breathing even a minimal quantity of smoke causes a big vein to appear on the nose of a Stand user. Captain Tennille immediately falls for it, and reveals that he is actually an impostor of the real Captain Tennille, who he had killed earlier in Hong Kong bay.

He tries to take the Runaway Girl as hostage, but before he manages to do so he is stopped by Star Platinum. The Imposter however drags Jotaro underwater with his stand Dark Blue Moon, where his Stand can fight at full power. He traps Jotaro into a vortex, attempting to slash him with Dark Blue Moon's razor scales. He even manages to create some sort of little Cirripede-Stands that drain energy from his opponents' Stands.

Finally, by exploiting Star Platinum's ability to stretch his index and middle fingers, Jotaro stabs the enemy Stand and rips half of his head, defeating him, but in a last ditch effort, Captain Tennille blows up the ship, leaving the protagonists to meet their next Stand encounter, Strength. Tennile, however, is left to die in the sea.

Stand
The Imposter's  lung capacity surpasses human average by three times, and through practice, he can stay underwater for more than six minutes without breathing. This, combined with his aquatic stand, clearly gives him the advantage in battles at sea. He tells the Joestar group that  the Tarot Card his stand represents, "The Moon", symbolizes trouble in water, lies, betrayal and fear of the unknown. When Dark Blue Moon first appears everyone fears the unknown stand user and wonder who is lying: the trustworth but rude Captain Tennille or the suspicious but seemingly harmless Runaway Girl. They are essentially betrayed by the one who could be most trusted as the Captain reveals himself to be the user of the dangerous aquatic stand. The card can also be interpreted as a psychological conflict and confusion, all which can be easily related to the story arc the imposter is featured.

JoJo's Bizarre Adventure (SNES Game)
The events from Dark Blue Moon occours on some different ways from the original story, as Imposter Captain Tennille uses his stand to ttacks the party within a water trap found in said building. Also, the Runnway girl is completely removed from the game, that means Imposter Camptain Tennile does not use her as a hostage to attack the team.

JoJo's Bizarre Adventure: Heritage for the Future (PS1/DC/Arcade Game)
Unlike the previous game, the events from Dark Blue Moon appears on the game with nothing removed. It appears as "quick-time-action" mini-game during Super Story, as the player must dodge all the attacks from Imposter Captain Tenille's stand. The mini game can be replayed on Gallery Mode (Oingo and Boingo's book).

Trivia

 * The imposter is the only unnamed villain from Part III whose name remained never revealed in supplementary merchandises, and he is still only known as «The Fake Captain Tennille».
 * Even though he doesn't appear in the OVAs, the method used to reveal his identity as a stand user in the manga is used for a different enemy: Enya Gail.