Mirror Monsters

The Mirror Monsters (ミラーモンスター Mirā Monsutā?) created by Yui as drawing made by her and her brother, Shiro Kanzaki, when they were young and gave them to her mirror-self to gain a new life. As these creatures have no true life of their own, they had to prey on humans to survive on their lifeforce. The only human they can not attack is Yui herself, whom they obey absolute like Kanzaki. However, Rogue Mirror Monsters who attack Yui is attacked either by Kamen Rider Odin or a loyal Mirror Monster who serves Kanzaki. But the majority of the monsters are contracted allies and the power source for most of the thirteen Kamen Riders, building their power by absorbing the energy of other defeated Mirror Monsters. But if the energy is not absorbed, it could reform into a new Mirror Monster.

Contract Monsters
Once a Mirror Monster is confined, it forms a Contract with the Rider who captured it. However, the Contract Monsters can turn on their human partners if their Vent Deck is destroyed or should they decide to quit being Riders and thus starve the monster of the energy it would receive from absorbing the energies of other Monsters. Contract Monsters do have a sense of loyalty to their human partners (examples include Darkwing, Blancwing, Deswilder, and Magnugiga) but at the same time some will get angry at their Rider when forced to do something they choose not to do (Dragreder and Gigazelle are prime examples mainly due to the attitudes of their Riders). Then, there are those who completely show utter hatred for their Rider. In Ohja's case, after acquiring Metalgelas and Evildiver; his monsters constantly attack him. However, his unstable mentality and wild personality is more than enough to tame all three of his "pets." Beforehand, Metalgelas and Evildiver loyally served Gai and Raia respectively.
 * (Ryuki)|Dragreder
 * 
 * Volcancer
 * (Ryuki)|Magnugiga
 * Genocider
 * Venosnaker (Ryuki)
 * Metalgelas (Ryuki)
 * Evildiver (Ryuki)
 * Destwilder
 * Gigazelle
 * Goldphoenix
 * (Ryuki)|Blancwing
 * Dragblacker
 * Psycorogue

World of Ryuki
The Mirror Monsters also reside in the Mirror World in the A.R. World of Ryuki. They often come into contact with the Kamen Riders of this reality. The Contract Monsters are specific Mirror Monsters that are contracted to the Riders in this world.
 * GuldThunder
 * Zebraskull Bronze
 * Megazelle
 * Negazelle
 * Omegazelle
 * Magazelle

Aside from Mirror Monsters in the World of Ryuki, the Raydragoons (レイドラグーン Reidoragūn?) are Dragonfly Mirror Monsters that live in the World of Negatives as Otoya's minions, taking the guise of normal humans. They are destroyed by Diend.

Dai-Shocker
As one of the races of the Nine Worlds, the Mirror Monsters are part of the Dai-Shocker alliance, a coalition of all villain organizations fought by the Kamen Riders, who have ambitions to conquer the multiverse.

The Mirror Monsters Sheerghost, Raydragoon, and Psycorogue, were part of the Dai-Shocker army that was fought and wiped out by a gathering of 25 Kamen Riders in the World of Decade after Dai-Shocker started their invasion of the worlds. Kamen Rider Decade: All Riders vs. Dai-Shocker

The Mirror Monster Solospider was a member of the Dai-Shocker remnant, Super Shocker, that appeared in the World of the Rider War.

Wild Monsters

 * Deadlemur
 * Gelnewt
 * Sonorabuma
 * Fake Kamen Rider Agito

Spiders
Though one type appeared in the show, many more human-like types appeared in the 13 Riders special. The spiders also aid other Spiders when needed during battles.
 * Dispider
 * Mispider
 * Respider
 * Solospider

Zelles
Humanoid gazelle monsters that usually attack in groups, sneaky and blindingly fast with the ability to jump distances. Despite being rogue mirror monsters, they usually travel with Kamen Rider Imperer because of his contract to Gigazelle.
 * Gigazelle
 * [[Megazelle
 * [[Negazelle
 * [[Omegazelle
 * [[Magazelle

Zebraskulls
Zebra monsters able to stretch their bodies, using the blades on their forearms to slice and dice prey.
 * Zebraskull Iron
 * Zebraskull Bronze

Boarders
Wild boar-like Mirror Monsters, they use their bodies as weapons in charge attacks.
 * Wildboarder
 * Shieldboarder

Biters
Longhorn beetle-like monsters armed with boomerang sabers.
 * Zenobiter
 * Terabiter

Krakens

 * Bakraken
 * Wiskraken

Guld
Kanzaki's bird-like Mirror Monsters, serving him in maintaining the Rider War by eliminating those who refuse to fight and those who get too noisy in his affairs.
 * GuldThunder
 * GuldStorm
 * GuldMirage

Abyss
Humanoid Shark Mirror Monsters that are able to use water based attacks. In Kamen Rider Decade, both of these shark Mirror Monsters are contracted to Kamen Rider Abyss.
 * Abysshammer
 * Abysslasher

Buzzstingers
Humanoid bee monsters that usually attack in groups. A trio of Buzzstingers first appear to target Mika, the only survivor of their attack on an ocean liner after being saved by Asakura to be used by him in order to feed his monsters. The trio used the "Trinity" attack to counter any Final Vent attack until they were all killed by Ohja's Veno Crash, Knight's Hishou Zan and Zolda's Giga Launcher from all three directions at once. Their essence was soon devoured by Venosnaker, Metalgelas, and Evildiver. A pair of Buzzstingers appeared in episode 37 to target Eri after she came out of her coma.
 * Buzzstinger Hornet
 * Buzzstinger Wasp
 * Buzzstinger Bee
 * Buzzstinger Broom
 * Buzzstinger Frost

Shereghosts
Mirror monsters that modeled after Dragonflies make their presence known in the Rider War end game in the TV series (41 and after) and Episode Final, where Yui's new life is almost used up. The Shereghosts (シアゴースト Shiagōsuto?) are a larval stage, able to shoot silk from their mouths to escape or capture prey. But the Shereghosts can molt into a mature Dragonfly form called Raydragoons (レイドラグーン Reidoragūn?). In Episode Final, the Raydragoons can assume large forms called Hydragoons (ハイドラグーン Haidoragūn?), which could be overpowered by Dragranzer and Darkraider.
 * Sheerghosts
 * Raydragoons
 * Hydragoons

Organization Alliance

 * Shocker
 * G.O.D
 * Geddon
 * Delza Army
 * Dogma Kingdom
 * Jin Dogma
 * Gorgom
 * Crisis Empire
 * Fog Mother
 * Gurongi
 * Lords
 * Orphnoch
 * Undead
 * Makamou
 * Worms
 * Imagin
 * Fangire
 * Dopant/Snooza Family
 * Yummy/Greeed
 * Zodiarts/Horoscopes
 * Phantom