Genocider

Genocider (ジェノサイダー, Jenosaidā) is chimeric Mirror Monster made up of EvilDiver, Metalgelas and Venosnaker.

Appearance
Obtained through a Unite Vent, Genocider appears as a merged form of Kamen Rider Raia's EvilDiver, Kamen Rider Gai's MetalGelas and Kamen Rider Ouja's Venosnaker. All three components of Genocider are contracted to Asakura (Kamen Rider Ouja) and are used as either intimidation or to perform a Final Vent.

Kamen Rider Ryuki
Genocider first appeared after Asakura contracted EvilDiver, & Metalgelas as well as his original contracted monster Venosnaker. On many occasions, Asakura would summon Genocider merely to indimidate the other riders and it would rarely be involved it in battle. When it was however, it commonly ran at the opponent and shot venom at them. Genocider played a role in the Death of Goro who had replacing Shuichi Kitaoka as Kamen Rider Zolda and the destruction of Magnugiga. It is unknown what happened to Genocider after Asakura died in the series. However, The end implies that he never existed afterwards.

Kamen Rider Ryuki: Episode Final
In alternate ending of Kamen Rider Ryuki, Asakura unites his monsters to form Genocider and aims to finish Femme off for good. He's interrupted by Ryuga, who summon Dragblacker to ram Genocider and caused Asakura's plan failed. Ryuga attacks him and trying to destroyed him with his own Final Event. But, Asakura able to evade the attack and the attack hit Genocider instead, destroying Genocider. This reverting Asakura as Ouja to his blank form.

Uses
Genocider plays a pivotal role in his Final Vent where a vortex opens up on his chest which then allows Asakura to kick his enemy into it, supposedly killing them.

Genosurviver
In a S.I.C. Hero Saga story, Asakura had hijacked almost all of the contract monsters and used the Unite Vent and Survive cards to turn them into Genosurviver. It is unknown what it's abilities are as it never appeared in the show. It only appeared in the first Ryuki's S.I.C. Hero Saga story in Monthly Hobby Japan magazine, Masked Rider Ryuki: Advent Calendar (MASKED RIDER RYUKI -アドベントカレンダー-, Kamen Raidā Ryūki: Adobento Karendā).

Trivia

 * Genocider's name comes from the word Genocide which means deliberation and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group as it mainly focused on Genocider's Black Hole ability which can suck nearly everything.