Kankrelats: These monsters are X.A.N.A.'s weakest ones. They usually attack in large groups. They are much faster than Bloks, and are fairly hard to hit because of their small stature.
Hornets: These are the first monsters that are capable of flight, and are one of the few to have more than one attack. They can fire rapid-fire lasers from their stingers and spray poisonous acid from their heads.
Bloks: They are one of X.A.N.A.'s most used monsters. Bloks have three different attacks: standard laser, rings of flame, and freeze ray (which can immobilize its target in ice, for a short time). However, with an eye on each side of their 'heads' (four in all), their major weakness is that hitting any eye can destroy them.
Krabs: They are generally found in groups of two or three. They can use their legs to stab their enemies, and fire strong lasers from their eyes. In the second season, they demonstrated the ability to project lighting blasts from under them. This is the only monster that can be destroyed by cutting off its legs.
Megatanks: These are one of X.A.N.A.'s strongest monsters. They are large and ball-like, whose armor is indestructible. They attack with a powerful laser that can runs straight in all vertical directions. To do this attack, it must expose its Eye under its armor, making it vulnerable in that moment.
Tarantulas: They were first introduced in New Order, they were depicted as X.A.N.A.'s deadliest monsters. They are excellent shots and are very durable. They can fire ray beams from the tips of their front legs; later, they can fire ray beams from their heads.
Guardians: They were used by X.A.N.A. to capture and imprison the digital avatars of the Lyoko Warriors, rather than devirtualizing them. They are immune to any type of attack, and the only known way to free the trapped Warrior is to create a false copy in order to trick it into releasing the real Warrior. X.A.N.A. only used them on two known occasions, potentially because it became aware of this flaw.
Creepers: They are found in the Carthage Sector. Creepers are snake-like monsters that attack by firing lasers from their mouths.
Mantas: The strongest flying monsters. They are large manta ray-like creatures with strong lasers, and can also defecate mines. They can fly through the air, but are slower than Hornets.
Sharks: Only found in the Digital Sea. Shark-like creatures that attack by shooting torpedoes from their mouths.
Kongres: Found only in the Digital Sea. They have the appearance of giant piranha eel monsters. They are the most common monsters seen in the Digital Sea and have only one laser weapon, which is fired from their eyes.
Kalamar: Found only in the Digital Sea. It attacks by latching onto its target and drilling into it.
Trollocs: The human sized monster robots that are half-human and half animal. They mostly appear as humanoid rams, boars, wolves, hawks, rats, bears, tigers, bugs, sharks and crabs. They fight like Barbarians and Mongols.
Hellhounds: These Monster robots resemble robot wolves with silver jaws and they have blood red eyes. These Dangerous beasts can sniff out anything like hounds. Demon wolves can appear as Black Wolves, Brown Wolves, Gray Wolves, Dobbermans, Rotwrilers, Bulldogs, Pitbulls and German Shepard Dogs.
Dluggas: Dluggas are monsters that are robotic monsters that are a third of a really ugly baby, a third of a Baboon and a third of a banshee. Dluggas can hypnotize their victims and make them do crazy and gross stuff and they can also scream so loud that buildings will shake.
Magma Slugs: Monsters that are robotic lava monster snails with a igneous rock shells that can burst out a blue flame that can destroy anything. They try to eat people by chomping at them randomly.
Scyphozoa: One of X.A.N.A.'s most valuable pawns. It has the appearance of a giant jellyfish and is very difficult to destroy. It has the ability to drain the knowledge, DNA, and life force from a victim with its tentacles, and can also implant a virus within its victim, and also possess its mind.
Kolossus: X.A.N.A.'s biggest and strongest monster ever. Created by drawing computing power from the hundreds of Replikas that it has established all over the Internet. It has the appearance of a giant fire and earth elemental being, with a sword replacing its left hand. Its body is indestructible and one attack from it results in instant devirtualization. The only way to destroy it was to simultaneously attack the Eye of X.A.N.A. on its head and its left sword arm.
Fan Made Special Monsters
Kankrelat King: A monster that looks like a really Giant Kankrelat with a king's crown on it. Unlike other Kankrelats, the Kankrelat King has giant metal Arms that weild bazookas that shoot missles at people.
Sumo Troll: A Giant Muscle Monster that looks like a robot Mountain Troll and a Sumo Wrestler wearing a Walrus cloak and Polar Bear tunic. It uses giant brass Knuckles that can cause an earthquake.