Zero Darkness

After Ultraman Belial's spirit successfully hijacks his arch-rival Ultraman Zero's body, Belial transforms into Zero Darkness, an incredibly powerful Fusion Ultraman. As Zero Darkness, Belial wastes no time in putting his new form's power to use and catches the Ultimate Force Zero off-guard, destroying their base and killing off Jean-bot in one fell swoop. Given Zero Darkness's remarkable strength and fearsome new abilities, the other members of the team aren't far away from meeting the same fate...

Example of:
Fusion Dance