Parasite Monsters are parasites that takes control of a person's mind. These parasites manifest in the host's Deck as the monster card "Fusion Parasite" and warp their strategy into one that utilizes Fusion Summon, regardless of their Deck's usual play style or the host's Dimension of origin. Despite their organic appearance, the monsters are advanced form of Real Solid Vision and thus require control from their cards to function properly.
Parasite Monsters are created by The Doktor with Leo Akaba's ARC System. They are developed to reside inside the host’s brain, allowing them to collect the host’s memory data and analyze them and have a strong control on the host's mind. The Parasite Monsters are programmed to make their hosts become loyal to The Professor. As seen with Celina, Rin and Lulu, the parasite monsters can make their hosts act as sleeper agents, allowing them to retain their normal personalities until the time is right. As seen with Lulu, the true nature of the parasite is to suppress the original personality of that person so that they lose control of their bodies and most of their consciousness. If there is a strong enough external stimulus, it is possible for the host to break free of the parasite temporarily. According to Aster, the host will be completely free from the influence of parasite when the Doktor is defeated. Defeating the host will not free them from the Parasite's control, whether or not their "Fusion Parasite" cards were destroyed during the Duel or if the host broke free momentarily.
Parasite Monsters are also able to quietly enter a host, as shown when one entered through Yuya's ear during his Duel with Celina and Lulu. At this point, however, it was also shown that Parasite Monsters can be repelled, as it invoked Yuya's awakening for a moment, allowing Z-ARC to immediately neutralize and destroy it.
- Celina (freed after the Doktor was sealed into a card.)
- Rin (freed after the Doktor was sealed into a card.)
- Lulu Obsidian (freed after the Doktor was sealed into a card.)
- Unnamed Duel Academy Student (freed after the Doktor was sealed inside a card.)
- Zuzu Boyle (freed after the Doktor was sealed into a card.)
- Yuya Sakaki (failed, destroyed by Z-ARC.)
- Yu-Gi-Oh! ARC-V episode 127: "Revival Zero"
- Yu-Gi-Oh! ARC-V episode 115: "Shiver Me Lancers"
- Yu-Gi-Oh! ARC-V episode 117: "Grip of the Parasite"
- Yu-Gi-Oh! ARC-V episode 119: "Family Face Off"
- Yu-Gi-Oh! ARC-V episode 118: "Survival of the Fittest"
- Yu-Gi-Oh! ARC-V episode 125: "Rise of the Parasites"
- Yu-Gi-Oh! ARC-V episode 123: "123 Fusion Destruction"