Genius

Genius monsters are Monsters in the Elder Tale universe that did not exist prior to the Catastrophe. They are the main antagonists of the Log Horizon TRPG, hoping to spread death and destruction around the world.

Overview
There are over 90 Geniuses in the world, but only some of them are active. However, those that are active caused the disappearance of almost all the Ancients and the Thirteen Chivalric Orders. Their abilities are above the scope of the world's laws, and they hold knowledge about the Adventurers' old world. The Geniuses' powers hold the secret to this world, and must be defended from by the Adventurers.

Currently, all the Genius monsters seem to be named after demons. Specifically, their name and powers are derived from the Nuctemeron.

Route 43 arc
Roe2 mentions the Genius monsters when talking to Minori during the invasion of Wyverns, saying that the Odyssea Knights' repeated suicides may be part of the monsters' plans, since it creates something called "Empathium."

Introduced in Dragonhowl Mountains
"Our duty is about to achieve a success. We cannot leave the corridors leading to the sky. It's really fun to torment those tokens that don't have self-awareness."
 * Rasphuia (ラスフィア)

- Rasphuia, Overseas Side Story chapter 6


 * A level 89 Normal monster, Rasphuia looks like a grotesque bisque doll with its head freshly cut off and the limbs bent in all the wrong places. Although her looks and words are elegant, she hides behind them a cruel personality. She moves like an insect, using her long, sharp nails to climb up and down trees. Her ability allows her to have multiple "Names", or souls, that take damage for her and almost instantly regenerate her when a body part is cut off.


 * Leonardo eventually defeats her by using Parallel Plot so quickly, he completely destroyed her head before she could regenerate.

"Fall as a sham. Stoppage is suitable for you. Cease your timeline, spawn of Nothingness!"
 * Papus (パプス)

- Papus to Elias Hackblade, Overseas Side Story chapter 9


 * A level 89 Normal monster, Papus is a mass of parasitic, acid-spewing tentacles wearing a robe. Coal tar-like bubbling puddle is always spread at its feet, and every words and laughter that Papus speaks are composed of a collection of popping sounds of bubbles. It is capable of controlling other Monsters by its tentacles.
 * Papus is most likely the cause of the Black Dragon's attack and the infection of a young Lander boy. One of the Chinese server's more famous guilds, the Lelang Wolf Cavalry, is wiped out twice by the Black Dragon, so Kanami's Party decides to take care of it. On their way to the mountainside, they are encountered by the Black Dragon, with Rasphuia and Papus riding atop it. Papus was aware of Landers and Ancients being created by personality software and nearly killed Elias Hackblade with his "words of death." However, Kanami snapped Elias out of it, and they kill Papus.

Introduced in the Log Horizon TRPG

 * Mizkun (ミズクン)
 * Mizkun takes the appearance of a human-shaped shadow. He specializes in providing logistical support and, thus, rarely comes out; he also has the power to brainwash demi-human Monsters. Currently, he is scheming to shut down the magic circuits guarding Adventurer Cities and overrun them with his brainwashed demi-human Monsters.
 * He is also called Mizkun of Shadows (影法師のミズクン)


 * Heiglot (ヘイグロト)
 * Taking the appearance of a beautiful woman in a white kimono with blue eyes, long hair, and black wings, Heiglot has powers over ice but has yet to master them. In particular, she specializes in wide-area attacks and aims to master her powers in order to cover the whole land with snow, which would be disastrous for crops and harvests.
 * She is also known as White Princess Heiglot (白姫のヘイグロト).


 * Mascarvin (マスカルウィン)
 * An Undead swordman wielding a large, black-bladed katana. He has black eyes and hair, and dons a black coat on top of black clothes. He has an ominous yellow aura that summons Undead Monsters. His prowess is in its swordplay, one of his greatest features being a continuous attack without any break. Furthermore, when someone looks into Mascarvin's eyes, a scene of his/her death is displayed in his eyes. He is hiding in a certain ruin located in the northeast region of Eastal. Around the ruin, the plants have withered and many undead monsters wander the area.
 * He is also known as Mascarvin of the Blade (刃のマスカルウィン).


 * Sachluph (サクルフ)
 * Sachluph is jade-colored giant owl that can fly noiselessly and attacks with sharp talons. Although he gives the impression of a sage, outside of battle, he has a jovial personality and likes silly jokes. Sachluph has control over the growth of plants, and can fire plant seeds at a target, sprouting seeds in the body. He suddenly appeared in the "Ocean of the Spore", a forest area close to Templeside City (Kichijoji in real world) and flew away. Now, he is flying around the Yamato server, promoting the growth of Fairy Rings and inciting plant monsters into attacking.
 * He is also known as Sachluph of Green Wings (緑翼のサクルフ).

"I know you Adventurers are hiding some delicious desserts. No matter how hard you try to live in peace, my mates never overlook."
 * Sislau (シスラウ)

- Sislau, TRPG Replay 2 chapter 4


 * Sislau is a main villain of TRPG Replay 2, professing himself as the "Genius of the Fourth Hour".
 * He is 'incarnated' as young fairy boy that is about 30cm in height and has butterfly-like purple wings. Although he has a contemptuous attitude, he himself has not meant to be deliberately offensive.
 * His wing scales are virulent poison that can taint lands, brainwash monsters, and give a semi-perpetual abnormal status "Pestilence". He polluted Cornu River that flows near of Akiba to brainwash Hill Giants that had ruled the "Plains of Bodarel" and make an army. He was eventually killed by TRPG players.
 * He is also known as Sislau of the Pestilence (疫病のシスラウ).