These bosses appear in game modes like Adventure Mode and Boss Rush.
Kings are bosses from Magic Touch: Wizard for Hire. They have magic scepters that they use to blast lightning at fighters. They wear armor that can't be damaged; the only way to defeat them is by popping all of their balloons, which are only vulnerable when the king is attacking. When they aren't attacking, they erect a magic force field around their balloons. They can also summon purple and golden knights to attack fighters.
Chain Lightning Blast
Web Lightning Blast
Triple Lightning Blast
The Machine is a giant robot from Test Subject Complete. It has two phases; the first phase it hangs on the ceiling and fights with mostly projectiles; the second phase it detaches itself and transforms into battle mode, in which it uses more powerful attacks.
MewTube Boss is the less successful brother of Nitrome Boss. He fights from his Kitty Copter and uses all sorts of crazy cat-themed attacks.
For MewTube Boss's attacks, see SSN2: Classic Mode#MewTube Boss.
The demonic king of the shadowy monsters that invaded the Warlock's village, the Demon Overlord seeks to spread darkness around the world. He uses dark magic and powerful melee attacks to fight, and even summons demonic bodyguards to attack fighters.
Nitrome Boss's Cubot has gone haywire and is now rogue, destroying anything in its path! It uses its arm cannon to fire bullets and can fly around with its rocket boosters. It also has a Charomat installed in it that can spawn enemies to attack fighters.
Orange Nose Enemy Spawn
Big Hat Pirate
The Big Hat Pirate is out for a bounty! He has three phases; first he fights from aboard his ship, from which he fires cannons and sends out parrots to attack fighters. Phase Two Has him hop off his ship to fight you one on one; he throws bombs and explosives of all kinds. Once he's defeated there, phase three begins. He returns as a zombie pirate and his attacks are more powerful now.
Gunpowder Barrel Roll
Pieces of Eight
All Phase One Attacks
All Phase One and Two attacks (buffed)
The robotic dragon-like general of the Triclopian army, this super-weapon is armed with bullet-cluster cannons and a super laser designed to level entire cities and wipe out opposing forces. It has several new abilities when you encounter it in SSN2.
The dark, armored knight that guards the Tiny Castle has grown much larger, and now has some new weapons and methods of fighting.
Flaming Hog Throw
Flaming Hog Roll
Flaming Hog Rain
Orange Enzyme Boss
The Orange Enzyme Boss is a monster taking on a ghostly form. It uses strong attacks, projectiles, and summons minions to help it fight in its appearance in Test Subject Swap, and does the same in SSN2. *Credit for this boss/character and all of its original attacks go to Test Subject fan and Klemen702.
Summon Throwing Orange
Grab and Squeeze
Grab and Hurl
Gooey Yo-yo Attack
Chomp and Slam
The evil king of the Dark Creatures mounted on a sinister cloud monster. He attacks with lightning and fire and can summon Bats and Dark Creatures to fight.
Dark Creature Spawn
Dark Creature Throw
An evil robot that commands an army of robots to dominate the world. She remains stationary but has many means of offense to defend herself. She can fire lasers, bombs, rockets, and even deposit robotic underlings to do her bidding.
A monstrous, gigantic Cyclops responsible for kidnapping the fair maiden in Double Edged. He attacks in both Double Edged and SSN2 by throwing boulders, slamming his fists around, and spitting up Skeletons that fight players.
These bosses appear on a stage and when defeated can benefit the fighter that defeated it in some way. They have less attacks than fully fledged bosses and only appear on their respective stages.
Appears on the Fat Cat World stage. Fires bullets and bullet clusters around the stage, safe spot is directly underneath him (best place to attack from). Easiest of the three bosses on the Fat Cat World stage. When defeated by a fighter, King Meka's bodyguards will focus their fire on other fighters.
The second boss on the Fat Cat World stage. Fires bullets in all directions and has harmful spines on its body. Safe spot is below and to the right of him. When defeated King Cacta will release bees that home in on other fighters.
The third boss and hardest boss on the Fat Cat World stage. King Shroom shoots bullets in all directions and spawns off Tree Enemies to attack fighters. When defeated, King Shroom lets off poisonous spores upon dying that deal poison damage to other fighters for ten seconds.
Talos appears on the Ancient Greece stage, attacking by stomping around. He can burrow fighters he directly hits and damage fighters by making the ground quake. Weak points at his heels. Upon dying he releases a ton of Enemy Soldiers that swarm opponents.
Appears in the Robot Factory stage. Leaps around and fires toxic blasts. Upon being defeated, Bigfoot leaves and then later returns and sneak attacks an opponent to K.O. them.
Appears on the Fortress of Steam stage in his Steam-powered Batter-Berger, spraying poison gas around the stage as he flies around. Upon being defeated, Baron Battenberg's Batter-Berger explodes and damages opponents caught in the explosion.
Appears on the Dr. Boshi's Base stage. Shoots bullets around and releases mines that home in on fighters. Upon being defeated he will electrocute and stun nearby opponents before dying.