The Familiar of Red Nova, also known as the Familiar of Scar-Red Nova or the Familiar of the Crimson Devil in the Japanese version, is a fire demon whose role is to be the servant of the Red Nova.
This demon planned to revive the Crimson Devil from his 10,000 year slumber, after its defeat at the hands of the Crimson Dragon, by offering Jack Atlas as a sacrifice to become the new avatar of the Crimson Devil.
The Familiar and the Red Nova implanted a dream in Greiger, where he saw Jack Atlas die, by relying on power. As a result, Greiger invited Jack Atlas to the Nazca region in the hope of overcoming this. He got Jack to Turbo Duel against Max. However, the Familiar possessed Max and changed his Deck. The Duel was halted when it became clear the Crimson Devil was at work.
Angry over the result of the Duel, Jack went to a village. Here, a villager informed him that the village had been abandoned due to the works of the Crimson Devil. The Familiar then appeared in its demon form, taunting Jack into chasing it. After running around the village, Jack was brought back to the villager, who was now possessed by the Familiar and accompanied by the Crimson Devil in the form of a flame. The Familiar identified itself as the faithful servant of the Crimson Devil and asked Jack what he desired. Jack replied that it was power and the Familiar offered Jack to join the Devil's side, saying that they would be waiting at the shrine. It left the villager's body, causing him to pass out.
When Jack arrived at the top of the shrine, he was transported to a hidden chamber. The Familiar told Jack that his master is locked away and has been waiting for Jack. Jack demanded the power and the Familiar offered it, under the condition that he and Jack perform the contracted ritual; if Jack defeats the Familiar in a Duel, the Devil will grant him overwhelming power. Jack agreed. Yusei, Greiger and Max followed Jack with Greiger informing Jack how they had all been used. However the ritual Duel had already begun as planned and the Familiar revealed that if Jack loses, his body will become host to the Crimson Devil and his friends will be fed to his master in the sacrifice.
The Familiar used a "Yomi" Lock strategy, which countered Jack's power strategy. Jack developed new tactics to fight back. When both players Life Points were low, the chamber began to fall apart and the Crimson Devil started to appear. However Jack used "Blazing Soul" to absorb Red Nova's power and create the card, "Red Nova Dragon", which he used to defeat the Familiar. The statue of Red Nova then fell over crushing the Familiar.
The Familiar of Red-Nova may be a reference to the Sons of Muspellheimr in Norse mythology who are fire demons. The Familiar of Red-Nova is also a fire demon.
The Familiar's most used power is his ability to possess people. It has been used on Greiger, Max and a villager in the series.
Another ability is to fire energy blasts from his hand, which he used to destroy the stairs and the exit to the Earthbound Immortal Shrine and to knock Yusei off his feet.
He was also able to destroy the floor surrounding Jack, trapping him in the center of the room, unable to reach anyone outside of the duel.
The Familiar uses a "Yomi" Deck. It uses cards that quickly inflict effect damage while protecting himself with various stalleffects. It consists of low LevelFiend-Type monsters that can be quickly destroyed to inflict damage.
Instead of cards, the Familiar uses tablets, similar to the tablets used in Ancient Egypt, which had monster Ka sealed inside them.
The Familiar took control of Max and Greiger to lure Jack Atlas into a Duel, where he used this Deck. It was given to Max by the Familiar whilst under its control. The Deck is centered around putting multiple monsters with the same name in the Graveyard to benefit from cards such as "Smoke Mirror" and "Ancestor Bird".