The Big Core Duo is the first and fourth boss in the game. It is a specially-modified Big Core. This Big Core starts with the same old Quad Shot attack, but then it transforms into a six-shot-firing and laser-sweeping havoc of a Core warship.
At first, the boss will be a normal Big Core and attack as it always has. However, after its defeat, it will take off to the background, and change into a different form by flipping over and opening its sides. This form will first attack by firing a spread of six lasers at you a total of four times, before firing a pair of powerful, continuous lasers that will sweep the screen with its movement. From here, it will repeat the process until it is defeated.
- In the updated version of the game, the boss music will change to "Fighter Blood", an arrangement of the Nemesis 3 boss theme, for the second form.
|Characters||James Burton (Vic Viper) • Gaudie • Venom|
|Stages||Volcano • Cell • Moai • Wasteland • Antichthon|
|Bosses||Volcano • Iron Maiden • Big Core Duo • Zub Rush • Crawler X • Moai Orb • Re-Bone • Enigma • Electronic Cage MK2 • Xaerous Brain|
|Big Cores||Big Core MK I • Big Core MK-I Rev.2 • Big Core MK II • Big Core MK II Kai • Big Core MK III • Big Core MK IV|
|Big Core variants||Beacon • Blaster Cannon Core • Bubble Core • Circle Core • Coreship • Crater Core • Crystal Core • Dellinger Core • Desert Core • Heaven's Gate • Juggler Core • Laser Core • Lizard Core • Neo Big Core • Perla Meralda • Rexion Core • Rolling Core • Shining Core • Super Big Core • Terra Core • Vanishing Core • Genocide Core • Odin Core|
|Core-style bosses||Abaddon Warship • Covered Core • Covered Core MK II • Dead End • Kraken • Mayhem Warship • Metal Slave • Misfit Warship • Queensrÿche • Riot Warship • Plate Core|
|Pseudo-Cores||Death • Death MK II (DeathDouble) • Death MK III • Beta Core • Nobil • Triple Core • Crash Bam|
|Tetran variants||Tetran (Zylom) • Covered Tetran • Crystal Core D-X02 • Laser Tetran • Tenny Rop|
|Parody Cores||Candy Core • Decoration Core • Decoration Core MK II • Viva Core|