Nightmare is a powerful entity and enemy of Kirby. He serves as the final boss in Kirby's Adventure and its remake, Kirby: Nightmare in Dream Land.
In these games, Nightmare takes control of the Fountain of Dreams in an attempt to extend his control over Dream Land. Trying to prevent this, King Dedede breaks the Star Rod and scatters it around Dream Land, temporarily leaving Nightmare unable to take control and seems to trap him inside the Fountain of Dreams. Kirby, unaware of Dedede's intentions, restores the Star Rod and places it back in the fountain. With the Star Rod back in place, Nightmare reveals himself. Nightmare and Kirby then fly into space. Kirby fights Nightmare (in orb form) and defeats him. Nightmare flees to Popstar's moon, with Kirby in close pursuit. Nightmare, now in his true form, re-engages Kirby but is again defeated when Kirby delivers a final blow which destroys a large portion of the moon.
Powers and Stats
Classification: Abstract monster
Powers and Abilities: Superhuman Physical Characteristics, Dream Manipulation, Flight, Teleportation, Regeneration, Darkness Manipulation, Reality Warping, Energy Manipulation, Geokinesis, Intangibility (Unexplored, but in the anime Kirby's fire beam and the Halberd's lasers simply phased inside of his robe into what seemed to be endless void), Immortality (Type 8) (As long as there is fear in the heart of people, he will someday return)
Speed: Massively FTL+ via power-scaling
Lifting Strength: Unknown
Striking Strength: Unknown
Durability: Multi-Solar System level (Appears to be immune to anything but Kirby's Star Rod and has some sort of intangibility, but it's possible he can be taken down by other means aside from the Star Rod or simply by overwhelming raw power)
Stamina: Superhuman, able to fight Kirby for an extended period of time
Range: Galactic (Was going to spread nightmares all around the galaxy)
Standard Equipment: None notable in the games, but has a monster-creating machine in the anime and an entire corporation full of them.
Intelligence: Unknown in the games, but quite manipulative in the anime, playing on Dedede's jealousy and selfishness to constantly sell monsters to finance his own goals of conquest.
Weaknesses: He is quite susceptible to the Star Rod.