Dai-Shocker
The mysterious Dai-Shocker (大ショッカー, Dai Shokkā?, "Great Shocker") organization is a conglomation of all villain organizations who set into motion a plan to take over all dimensions due to someone providing the means to do so. Based on the World of Decade, their insignia is double-headed version of Shocker's eagle crest, but with the "DCD" written on it that hints at Decade's ties to them. In addition to Doctor Shinigami and Doktor G, there are many other members of Dai-Shocker that come from previous Kamen Rider Series. They sent their agents out across the worlds for universal domination. During the events of Kamen Rider × Super Sentai: Super Hero Taisen, Tsukasa Kadoya reforms Dai-Shocker and becomes their Great Leader once more in order to take down the Super Sentai teams and the Dai-Zangyack group led by Captain Marvelous. However, it is revealed that it was a plot between Dai-Shocker and Dai-Zangyack all along to have the Super Sentai and the Kamen Riders wipe out each other. Both groups of villains are defeated after Tsukasa and Marvelous reveal to them that they knew about their scheme all the time, having the heroes they supposedly "destroyed" sent to an alternate dimension and summoned back all together for the final battle with them.
Read more about this topic: List Of Kamen Rider Decade Characters