Here, I'm going to show some important villains in this story.
Name: Razen Cladis. ("Razen" means: Rage)
Villain Name(s): Kamen Rider Dark Decade. Kamen Rider Another Dark Decade.
Other Names: The New Destroyer of Worlds. The Black Decade. Negative Nick. Negative Decade. Nick.EXE. Decade.EXE. ALTERNATE Nick. ALTERNATE Decade.
Species: Human(?)(.EXE/ALTERNATE)(may be a different species depending on what dimension he's in).
Home World/Reality: Earth (Dimension-1218).
Equipment:
DarkDecadriver.
Rider Cards.
Backstory: The physical manifestation of Nick's darkness from all of the pent up and suppressed anger from being bullied during high school. He later separated from Nick and now seeks to kill him, despite knowing that he can't exist without Nick being alive. He later turns into an Another Rider version of his Dark Decade form.
Name: Hundred
Backstory: An evil organization that invades other parallel worlds with the Aurora Curtain. They can copy the powers of Kamen Rider through their advanced technology, allowing their members to transform into them. After the deaths of the Hundred Four, Hundred began to create monsters called "Another Riders". Razen formed an alliance with them to hunt Nick across the Multiverse.
Names: Atropos, Clotho, and Lachesis.
Villain Names: The Three Dark Sisters.
Species: Homunculi.
Home World/Reality: Earth (World of Gotchard).
Backstory: A trio of Homunculi from the World of Gotchard, but were revived by the Hundred Superiors in order to dispatch Another Riders to invade parallel dimensions.
Name: Another Riders
Backstory: Kamen Rider-based monsters that Hundred created to serve them in invading other dimensions. They can only be destroyed by someone who can either transform into the respective Rider that the Another Rider is based on, or someone who can access a form based on the respective Rider.
Name: Kasshine.
These are the Foot Soldiers.