The Skull Brothers (スカル３兄弟 Sukaru San Kyōdai?, "Three Skull Brothers") are the main antagonists and final bosses of Bubble Bobble Part 2. They are the three parts of the Super Skel-Monsta's soul that split after his demise in Rainbow Islands. Individually, the three Skull Brothers are referred to as the Green Skull Brother, the Blue Skull Brother, and the Red Skull Brother.
Each of the Skull Brothers resembles an ordinary Skel-Monsta, however, they appear more ghostly in appearance, having only empty sockets for eyes and sporting ragged cloaks. Each Skull Brother also has a glowing light below their heads on the torso area of their cloaks.
While the Skull Brothers appear nearly identical to one another, only differing in terms of coloration, the Red Skull Brother is shown to have a red fire-like aura surrounding him. In his initial appearance in Parasol Stars, the Red Skull Brother's cloak is orange in color and he is surrounded by a green aura instead. The Red Skull Brother's second form appears much larger, and sports a skeletal body, as well as visible pupils and numerous cracks in his skull.
Each of the Skull Brothers is able to wield magic, and each brother has a different attack patten. The Green Skull Brother attacks by shooting a spread of three fireballs at the player. The Blue Skull Brother fires a magic spell at the player, shrinking them and preventing them from shooting bubbles. The Red Skull Brother does not attack the player directly in his initial form, instead firing hearts at the other Skull Brothers in order to restore their health. The Red Skull Brother's second form hops around the level, and can summon a Skel-Monsta and send it after the player.
As detailed in an unused ending text crawl to Rainbow Islands, the Skull Brothers were formed after the demise of the Boss of Shadow (in the form of the Super Skel-Monsta) at the end of his battle with Bubby. The Super Skel-Monsta's soul escaped from his body and split into three parts, each of which eventually formed into the three Skull Brothers. After some time (one hundred years later in the original Japanese story of Bubble Bobble Part 2), the Skull Brothers finally begin to take revenge on Bubby and Bobby, forcing the duo (or their descendants, Cubby and Rubby, in the Japanese story) to take action once again.
The Red Skull Brother first appears in Parasol Stars, taking the place of the Skel-Monsta as the time limit-enforcing enemy. He appears when the player takes too long to finish a level, and only disappears if the player loses a life or clears the stage. Like Skel-Monsta, the Red Skull Brother is invincible, and cannot be defeated by conventional means.
In the game's manual, the Red Skull Brother is referred to as Death (死神 Shinigami?, "Death God").
The Skull Brothers are properly introduced in Bubble Bobble Part 2, where they serve as the main antagonists. In the game's introduction sequence, the Green Skull Brother commands two Drunks to kidnap Judy, a friend of Bubby's, as the two are relaxing by a tree. This causes Bubby to transform into Bub in order to give chase to Judy's kidnappers. The Skull Brothers proceed to unleash an army of monsters on Rainbow World, causing Bub and Bob to set out to stop them and rescue Judy.
The Green Skull Brother appears the first boss of the game's fourth world, the Castle of Fire, appearing on level 70. The player is given a Snow Tonic to defeat him with, and after taking enough damage, the Green Skull Brother retreats, allowing the player to free Judy from her bubble prison.
All three Skull Brothers are fought on Level 80, acting as the game's final boss. The player is once again given a Snow Tonic to defeat the Brothers with. The Green and Blue Skull Brothers attack with fireballs and shrinking spells, respectively, while the Red Skull Brother provides the other two with hearts that restore their life. After the Green and Blue Skull Brothers are defeated, the Red Skull Brother transforms, appearing much larger and sporting a skeletal body. In this form, the Red Skull Brother can conjure Baron von Blubba to hunt down the player. After being defeated, the Red Skull Brother Bursts into flames, and Bub and Bob are changed back to their human forms by a fairy.