Nightmare Luffy was Luffy’s form after he was greatly powered up by one hundred shadows implanted into him. With Luffy’s strong spirit, he managed to contain one hundred shadows within him when most normal people could only contain two or three. In this form, Luffy was several times bigger than his normal self, and his skin turned completely blue. He was roughly the same size as Moria, and his body was similar to Chopper in Heavy Point. Luffy also talked differently, losing his usual carefree tone and instead speaking with a grim seriousness.

While in this form, Luffy could use the combined strength and skills of the shadows within him. With this strength, Luffy stopped a giant Gomu Gomu no Rifle attack delivered by Oars with one hand and unleashed massive attacks onto the zombie behemoth He could also move at incredible speeds, having safely rescued Nami and Usopp from a rampaging Oars, which was only made clear when Luffy made his presence known. Because one of the shadows belonged to a swordsman, Luffy also gained the ability to fight with swords, something he never knew before.