Ken performs a high-rising, spinning version of his Shoryuken/Heavy Shoryuken, with flames swirling around his fist and a large pillar of fire encircling him. The nature of this Final Smash allows him to hit multiple targets more reliably than his other Final Smash.
Shinryuken first appeared as Ken's second new Super Combo in the Street Fighter Alpha series. When performed, players could also repeatedly mash buttons to add more hits to the attack. This move carried over to many of Ken's appearances including as a selectable Super Art in Street Fighter III and in many of the crossover games that Ken happened to star in. According to story, Ken created this move to honor his and Ryu's mentor Gouken, who was believed deceased at the time.
Shinryuken also served as Ken's first Ultra Combo in Street Fighter IV, although the move in its original form would only appear if Ken whiffed the opening hook punch. If said punch connected, Ken would perform rapid kicks on his opponent before performing the Shinryuken itself. It also made a return in Street Fighter V: Arcade Edition as Ken's second V-Trigger.
The Marvel vs. Capcom series version of Shinryuken had Ken's fist wrapped in a large number of swirling flames while a large fiery pillar surrounded him, a visual effect done to match the comic book atmosphere of the series itself. Its also this version that the Super Smash Bros. Ultimate rendition of Shinryuken is modelled after. Ryu can perform this super in the first Marvel vs. Capcom game when switching his moveset to Ken's.
Ken's "Violent Ken" counterpart can also perform the move in SNK vs Capcom: Chaos as a regular Super as opposed to the limited-use Exceed that normal Ken has the move as.