Oni

"I shall grind beneath my heel all that exists"

- Super Street Fighter 4 Arcade Edition

Oni is a secret character in the Street Fighter series, seemingly based on Gouken as when you study the basis of his attack, it resembles Gouken's moves. He is more muscular, has lumps on his forehead which appear to be the early stage of horns, and is more dangerous than Shin Akuma. Leaked images of upcoming DLC Achievements for the Xbox 360 version of Super Street Fighter IV indicate that he will take the form of a new secret boss in Arcade Mode, as well as being a playable character. This "ultimate" form allows Oni to use an air dash and grants him new attacks such as a forward teleport which slashes at the opponent as Oni passes. Little is currently known about him. This should not be mistaken as Shin Akuma.

Super Street Fighter IV
Main article: Super Street Fighter IV

Oni appears to possess an air dash attack, the direction of which is determined by the punch button pressed. He also possesses a dashing slash which allows him to pass the opponent by, similar to his Ashura Senku. He also possesses a jumping smash attack which has been compared to Honda's Sumo Smash. It also appears that he no longer possesses his Hyakkishu attack.

Whenever Oni wins the fight, he interacts with the opponent's character, CPU or Human. He picks them up by their heads, then (offscreen) smashes their head into the ground, supposedly killing them. It is unknown whether or not he does this with every character, but it is likely. It should also be noted that this is the only character in the game that interacts with the opponent when they lose.

His Super Combo, the Raging Demon, remains intact, but now can be used in mid-air. His Ultra Combos are new and appear to be based on Super Arts from Street Fighter III: 3rd Strike.

His first Ultra Combo, Meido Gohado, is an advanced Messatsu Gou Hadou that can be fired from the air, but will not cause an animation if it is done in the air. On the ground, if the projectile connects on the first hit, the animation features Oni forcing his opponent back with the first projectile then blasting them with another, with the force of the projectile emitting energy from behind the opponent shaping into Oni's kanji character.

His second Ultra Combo, Tenchi Sokaigen, appears to be a precursor to his Kongou Kokuretsu Zan attack, where he only forms an eruption of energy in front of him, but if he hits square on the first hit, the opponent is launched up into the air, and Oni follows them up with a severely-powerful Shoryuken to the opponent's exposed back.

Trivia

 * In Japanese mythology, an Oni is a type of Ogre or Demon. This serves as a connection to both the names Gouki (Essentailly Strong Oni / Strong Demon) and Akuma (Devil). He may also be an official version of the fan based version of Akuma called Ogre Akuma, most notable as a character in MUGEN.
 * In the recent(leaked) Trailer for Evil Ryu and Oni, Oni claims that he is not human.It is possible that Oni is Akuma possessed by the Satsui no Hado