First, the user puts both of his hands in front of him, palms open and hands turned up at approximately a 90 degree angle. Then, he fuses together the tremendous energy of the Super Kamehameha into a Big Bang Attack that explodes into an extremely powerful stream of ki.
Vegito uses an attack similar to the Big Bang Kamehameha during his battle against Super Buu. The attack is powerful enough to destroy Super Buu's left arm, part of his antenna, and the bottom half of his body. However, Super Buu manages to regenerate from the damage he received and continues the fight with Vegito.
Super Saiyan 4 Gogeta uses the Big Bang Kamehameha during his battle against Omega Shenron, the product of Syn Shenron's absorption of the seven Dragon Balls. After reversing Omega Shenron's Negative Karma Ball into a positive blue energy sphere to dispel the veil of negative energy covering the Earth, Gogeta declares that he has only one more task to perform. He then fires the Big Bang Kamehameha at the Shadow Dragon, seemingly killing him. However, Omega survives, but in his Syn Shenron form; the force of the attack has caused him to regurgitate all but one of the Dragon Balls. Sensing victory, Gogeta tries to use the Big Bang Kamehameha again to finish off Syn Shenron, but because of the tremendous power he possesses (and because Gogeta plays around too much during the ten minutes of fusion), he defuses back into Goku and Vegeta before he can launch the finishing blow.
Appearances in games
In some video games, Gogeta's ultimate attack is the 100x Big Bang Kamehameha, a much more powerful version of the move which deals a high amount of damage. In the anime, Gogeta only uses this technique while in his Super Saiyan 4 form, but he can use it in his Super Saiyan form as a super attack in Dragon Ball Z: Shin Budokai, Dragon Ball Z: Shin Budokai - Another Road, Dragon Ball Z: Buu's Fury, Dragon Ball Z: Budokai Tenkaichi 3, Dragon Ball Z: Tenkaichi Tag Team, the Raging Blast series, Dragon Ball Kai: Ultimate Butōden, and Dragon Ball Z: Ultimate Tenkaichi. In Shin Budokai - Another Road, rather than being fired like a beam, it is fired like a short burst. It appears as Super Saiyan 4 Gogeta's Special Attack in Dragon Ball Heroes.
In Budokai Tenkaichi 3 and Tenkaichi Tag Team, this attack is the only Blast 2 attack that can travel through a Super Explosive Wave and harm the person using it. In fact, Big Bang Kamehameha, Gohan's Father-Son Kamehameha and Bros. Kamehameha, Super Vegito's Final Kamehameha, and Super Perfect Cell's Solar Kamehameha are the only Kamehameha waves that are strong enough to pass through Super Explosive Waves.
In Dragon Ball: Xenoverse, the Big Bang Kamehameha appears as one of Super Saiyan 4 Gogeta's Super Skills. This version is harmless if it isn't charged up properly, and doesn't have the range of predecessors, but makes up for these short comings in raw power. The attack will also absorb energy blasts while it is charging. Gogeta's X100 Big Bang Kamehameha variant also appears as an Ultimate Skill. The Future Warrior can obtain Big Bang Kamehameha Super Skill as a reward in Parallel Quest 49: "Saiyan Revolt". The Warrior can also obtain the 100x Big Bang Kamehameha as a reward in Parallel Quest 54: "Saiyan Warriors".