|Commanders|| Fedeln Metzelei|
|Headquarters||Meteor Crash Site|
|Area of Operations||Inner Solar System|
|Enemies With|| Regular Army|
|Affiliated With||Martians (Metal Slug Defense)|
They appear as large, toad-like creatures, with bulbous heads and reptilian features. Their technology appears to be organic, as seen when certain vehicles leak a purplish blood-like fluid when destroyed. Certain members of the species are gifted with insect-like wings, and the ability to launch corrosive plasma blasts from their mouths. Their society is hive-based, with rank based on skin color and durability. They are led by the massive "Invader Queen", the final boss of Metal Slug 6.
They may very well eclipse the Martians in viciousness. They are also the natural predators of the Martians; Mars People cower and panic when the drones appear.
Drones: The most commonly encountered Invader strain. Able to breed maggot, which slowly home in on a target and explode. Sometimes they spin around or use their long arms to head smash the player. The ones in final mission explode into a bunch of maggot after death. Gray in color.
Squad Leader: Pink in color, and much different than other Invaders. Once they appear, they begin to spin around, and then bounce around the field, only affected by walls. They sustain more damage and produce a bunch of larvae after death. In Metal Slug Attack, they are called Ravenous Invaders.
Flying Drones: The most common encountered Winged Invader. In the beginning section of Mission 4, they spit one plasma blast at you. Gray in color.
Elite Troopers: Tan-Peach in color and only founded in Rootmars' route. they spit out three unguided plasma blasts.
Troopers: These Winged Invaders spit two unguided plasma blasts. Normally found in the air segment of Mission 4 (colored green), but they are also found coming up the pit once you prepare to start the Rootmars path (colored gray).
Squad Leader: A very rare Pink-colored Drone spitting out up to eight unguided plasma blasts.
Flying Parasite: Small, orange octopus-like creatures with the ability to take control of another organism, latching onto the victim's head with its tentacles and turning him/her into a zombie-drone with purple skin. Able to fly. When swooping down to take control a victim, it can also latch on to you if you get in its way. Once it successfully latches on to you, it will suck the player out until their clothes remain, unlike the NPCs which they control instead of killing.
Friendly Flying Parasite: Purple versions of parasites, who carry items and (to a lesser extent) supplies. They are only seen in Mission 4.
Hunter Walker: Fish-like anti-personnel creatures with four legs with a blue, oval-shaped body. They have a single cyclopian eye in the center of its body, scanning the area, just below their very large mouth. They are found in the last two missions. On the ground they spit spores three times in a row. However, the ones found in Hive occasionally are on the ceilings and drop eyeballs down at you, regenerating their eyes at an unnatural rate.
There is also a golden version in the hive that does not attack players and yields a 50,000 point reward upon death (one shot kills it). However, it is considerably faster than the other Hunter Walkers.
Hunter Lord: A giant version of the Hunter. It can release bombs across the screen, these giant creature have thick skin, making them immune to any weapon and it's eye is only weak point. A gray one is also encountered but it cannot be killed, nor does it attack players. In Metal Slug Attack, the Hunter Lords are called Giant Hunter Walkers.
Scavenger: Gray-colored scorpion-like Invader breed found in the subterranean section of Final Mission. They dig with their forearms and become yellow to charge toward a player.
Smasher: One-eyed, red, crablike creatures with four legs and a white chubby body. They spin their legs like helicopters when flying. When a target is below them, they inflate their body and plummet down in an attempt to smash them. They are seen in the Invader Hive.
Great Mother: The mother to all the Winged Invaders. It carries a massive reproductive system on itself, and flaps its wings around to move, albeit very slowly. Its appearance is grotesque and the flapping of its wings causes fear among all in the cosmos.
UFO: An unusually shaped Invader spacecraft used by unwinged Invaders. Attack by firing purple energy laser 3 times in a row, aimed at the player.
Flying Core: Flying Core. An object used by the Invaders that lifts surrounding objects and tosses them at its foes. It can throw single, multiple, or all the objects at you. It can also fire a flurry of green bullets. One is found near the end of Mission 3 throwing garbage, and the ones in Mission 4 throw large meteorites.
Flying Shelt: Indestructible Invader Flying Object, they look like giant rocks. Other than their meteor launchers, they cannot be destroyed; they can also crush you. Many crash-landed Flying Shelts can be seen in Mission 3 if you take the upper route instead of the lower route.
Crab-Tank: A kind of Invaders walker. Crab-like, it can fire two energy cannons from the nodules in its head. It is also open its head to to fire a large blue bouncing bubble which splits into 3 smaller ones from a cannon underneath its carapace.
Vanguard: A modified crab-tank with two tentacles atop its carapace. It is able to fire oval lasers from its guns in the first segment of the Final Mission, and the ones found in the Invader Hive fire a huge spinning laser from its eye, which can be hard to dodge. It is seen in Hard Mode only. In Metal Slug Attack, there is a "Type-A" Vanguard; it is essentially smaller and weaker than the standard Vanguard, but makes up for it with its fast speed. The Type-A Vanguard was built exclusively for Annette.
Controller: A green robotic variant of the parasite, a specimen of this type can control a host from afar, using a long umbilical cord attached to the victim's neck. It serves as a prelude to the last boss by taking over one of the characters that the player has not selected. The character varies, but each character has different habits.
These Invaders are stronger than the rest of their brethren and are capable of vocal communication. They have the ability to shapeshift into human form, but can also transform parts of their bodies to attack or defend themselves. Transformed parts of their bodies tend to be purple in color. When severely injured or killed, they burst into blue flames and melt.
All of these Invaders only appear in Metal Slug Attack.
Odette: A soldier in the Invader army who is tasked with learning about Earth's culture. She's somewhat carefree, often requiring reminding by her sister Annette, though she will complete the task given to her.
Annette: A prominent Invader officer. She's impulsive and hasty, but cares for Odette (who's her younger sister), giving her positive reinforcement to ensure she completes her tasks.
Nowan: A soldier who specializes in mimicry - one of the best among the Invaders, though they are also cruel and because of their mimicry skills, Nowan has no memory of its true name, form and gender. Appears as a young girl since it is the form it remembers the most.
Schwarz Metzelei: A powerful soldier of the Invaders, and one of four the Metzeleis. Has an insatiable appetite, and can consume almost anything as long as it has blood of some sort.
Fedeln Metzelei: A soldier who's often isolated from the rest of his allies due to his lethal, uncontrollable poison. As a result, he has a somewhat weird personality. He's also one of the four Metzeleis.
Rillacle: A soldier who's more interested in battling rather than learning Earth's culture. Enjoys playing the game "rock, paper and scissors", though her vision is drastically different compared to the game itself.
Franke: A former human scientist who admired the Invaders so much that she grafted half of an Invader onto herself. She's somewhat mad and wants to create a new breed of human-invader hybrids like herself. She uses an advanced battle suit since she is not as good in hand-to-hand combat like the other prominent Invaders.
- The Invaders are based on both the Xenomorph aliens of the Alien franchise and Zergs from the Starcraft series.
- In the Final Mission, the Invaders' hive consists of 5 parts. The first part is where the Rebels are present. This is followed by the Hunters' Hive, which you have to dig down to reach. After that is the Invaders' hive, and the Final part is where you fight the final boss.
- Before their official name was given, fans always referred to them as Venusians or, less frequently, Jupiterians.
- In Metal Slug Defense and Metal Slug Attack, the Invaders are in the same faction as the Martians; both being classified as a "space army".