The Amadeus Syndicate is an evil corporation and terrorist organization serving as the main antagonist of Metal Slug 4. With the money they were able to obtain from their banks around the world, they became a very rich company. They are allied with the Rebel Army and assisted them when they lost their funding (after the events of Metal Slug 7/XX) by supplying the Rebel Army with more troops, weapons, and vehicles.
Their infantry has the same base sprite as ordinary Rebel Soldiers. They also have blue-suited that are better equipped than their green counterparts, suggesting they are some kind of Special Forces unit or honor guards.
- Amadeus Scientists
- White Baby
- Iron Fortress
- First Baby
- Sweet Baby
- Pirate Soldiers
- Numerous Amadeus Infantry
Vehicles and Technology
Most of the Amadeus syndicate vehicles and technology originated from Metal Slug 4 while some appeared at Metal Slug Defense and Metal Slug Attack and have received a variation.
- M-15A Bradley
- 3-Ton Utility Truck
- Prototype Iron
- MH-6s Masknell
- Melty Honey
- NOP-03 Sarubia
- Flying Tara
- Hammer Yang
- Amadeus Robot: A helper robot used by Amadeus Syndicate. Its sensor can fire energy blast.
- Morden Robot: A mass-produced cyborg clone of Donald Morden. Like the general himself, these robots are armed with a bazooka. When their cyborg body are exposed, they will act more like an undead zombie, possessing suicide attacks.
- Mecha Allen: A cyborg copy of Allen O' Neil which surprisingly exceeds Allen O'Neil himself. This model is fought as the penultimate boss of the final mission.
- Valerian Bears: These teddy bear-looking bipedal weapons are created by White Baby. All appears to be feminine and have 3 different variations: Rosa, Bubu, and Viola. Rosa specializes in long-ranged combat, while Bubu specializes in poisoning her enemies, and perhaps Viola is adapted at close-range combat.
- Brave Guerrier: A large airship used for troop support. It is armed with homing missiles and a minigun at the front cockpit, the central part consists of a large homing missile which appears at the Amadeus insignia, and the rear part of the blimp are two manned turrets along with a bouncing mine launcher. Despite being seemingly destroyed at the end of Mission 1, it reappears at Mission 5, supporting Sea Satan with missile blasts, whether it can be unmanned or remote-controlled remains unsolved until in Metal Slug Attack where it was later revealed that the blimp was controlled by an artificial intelligence.
Its design is heavily based on the Hindenburg airship.
- Toschka Dalanue: A large vigilance tower consisting of 5 parts: a horizontal cannon (5), a missile launcher and a Bazooka Soldier (4), twin cannons that emit fiery balls in a trajectory path, a bunker that summons Rifleman and Bazooka Soldiers, and lastly the upper tower operated by a Mecha Allen which shoots down parachute bombs and a large cannon. Its design is heavily recycled from the space rocket from Metal Slug 3.
- Iron: An improved version of the Iron Nokana, now armed with better homing missile launchers and an extendable propeller blade. This armored vehicle is manned by a Morden Robot.
- Big John: This giant mechanical puppet was once used as an attraction in a horror-themed amusement park until the Amadeus Syndicate repurposed it into a weapon, turning everyone in the park into zombies or mummies. It is armed with a mechanical claw and a missile launcher left-arm that can also summon vials of zombie virus.
- Sea Satan: Also called the "Sea Devil". According to Metal Slug Attack description, it is said to be based on the Morden's Army submarine 'Hodumi'. Used in destroying naval ships, it is armed with a turret manned by a Rebel Infantry along with missile launchers. Metal Slug Attack also introduced an airborne version of the submarine known as Sea Satan+, similarly to the Hodumi+.
- Amadeus Mother Computer: The Doctor's personal technology. It is divided into three mother computers:
- Amadeus Type Alpha: Number 17, this mother computer is armed with homing missiles, a mechanical claw and energy beams.
- Amadeus Type Beta: Number 18, this mother computer is similar to Type Alpha, albeit colored pink. It is also armed with a mechanical claw although its weaponry has been changed: the Type Beta now is armed with two Gatling guns, a large circular saw, and flying pods.
- Main Computer: The central computer armed with numerous energy and laser beams. It can also summon Amadeus Robots to aid it. Metal Slug Attack later reintroduced the central computer as Doctor Type: AI in which it is manned by an AI clone of the Doctor.
- Amadeus is a theophoric given name derived from the Latin words ama – the imperative of the word amare ('to love') – and deus (god). As a linguistic compound in the form of a phereoikos, it means "Love God!". The German-language equivalent is "Gottlieb'; Slavic versions include "Bogumil" and "Bohumil". Other related names are the female form, "Amadea", the French "Amédée (fr)" (male), the Spanish "Amadeo", the Italian "Amedeo", and "Amadis". In contrast, the Greek name "Theophilos" means "friend of God".