The Sea Satan is a huge submarine used by the Amadeus Syndicate. It can stealthily destroy ships or aggressively engage them head on. It can also kill any personnel aboard using its Gatling gun and dissipate its target using its missiles.
There will be Rebels getting out of the ship during the fight trying to prevent the player(s) from damaging and destroying the ship. The right side of the Sea Satan has a Rebel soldier manning a missile launcher/minigun. The flashing missiles provide items when destroyed.
After some time, the Sea Satan will dive under the sea and begin launching five TM-1L missiles from below. The Sea Satan also gets support from the Brave Guerrier during the fight by firing missiles horizontally.
|Sea Satan: The original Amadeus submarine.|
|Sea Satan+: Based on the Hodumi+, it is the original submarine modified to hover in midair. Large missiles pop out from the sub's hatch.|
|Sea Satan II: Painted purple variant to match the Amadeus Syndicate's colors. Unlike its floating predecessor, it uses its jet engines to burn enemies below.|
|Sky Satan: The Amadeus flying submarine with an all-blue accent scheme. It fires its large missiles from the sub's hatch, but its glating cannon fires flying guided mines like the Iwa Oh instead of bullets.|
|Desert Satan: A variant painted yellow and red. It is modified to to travel under the ground, and it can sink and emerge from the sand. Like the Sky Satan, It fires its glating cannon fires flying guided mines, and fires a huge amount missiles from the sub's hatch direct to the enemy.|
- Like all Metal Slug 4 bosses, it was made using old sprites from previous Metal Slug games.
- The Rebel soldier who controls the missile launcher was previously an unused sprite from the first game where helpful Regular Army soldiers would have controlled various turrets.
- Although the Sea Satan's concept art depicts a large submarine from below, the Sea Satan + instead has a smaller main body with the missile launcher protruding at the front. This is probably because the original body is way too large to hover.