Nightmare

Spooky!

Nightmare is a final boss character in the Kirby series. He only appears in two games, Kirby's Adventure and its remake. Nightmare is responsible for corrupting the Fountain of Dreams and attempting to spread nightmares. King Dedede tries to stop Nightmare from succeeding by breaking the Star Rod, but Kirby unknowingly restores it and thus has to defeat Nightmare.

Physical Appearance
Nightmare begins the fight in his Power Orb form. In this form, Nightmare is a dark sphere covered in silver, glowing stars. A gradient runs across the sphere: the top of the sphere is dark blue while the bottom is dark pink. This design remains the same between both the original game, Kirby's Adventure, and it's remake.

After Kirby defeats him in his orb form, Nightmare reveals his true form. In this form, Nightmare resembles a wizard wearing a spinning, tornado-like robe. In the official art for Kirby's Adventure and the anime his robe is covered in stars, just like in his first form. In the actual games, Nightmare's cloak is simply a dark purple shadow-like robe. Underneath his cloak is his weak spot, a tornado-like accumulation of darkness, and in some games, when he swoops, his body looks like a scorpion or lobster body. In the original game, Nightmare has two silver shoulder pads, and a small red medallion around his neck (obscured by his chin in-game). In the games Nightmare has human-like teeth, while in the anime his teeth are sharp and jagged.

In Kirby: Nightmare in Dream Land, Nightmare's second form is slightly changed. He now has a total of four shoulder pads instead of two, and much longer horns on his helmet. His chain and medallion are now both visible during the fight. He is also almost as tall as the screen now.

Kirby's Adventure and Kirby Nightmare in Dreamland
Nightmare is a powerful entity that serves at the final boss in both Kirby's Adventure and its remake. In both games, he can only be defeated by the powerful Star Rod that Kirby collects in both games.

In Kirby's Adventure, Nightmare takes control of the Fountain of Dreams in an attempt to extend his control over Dream Land. Trying to prevent this, 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 and fights Kirby.

In his initial form Nightmare, for the most part, stays on the right side of the screen, shooting stars at Kirby. The entire battle takes place in space as the two are falling back to Pop Star. As such, if Kirby doesn't deplete Nightmare's health bar in time he will crash into ground. After the final blow is struck, Nightmare retreats and flies to Pop Star's moon. Kirby follows him using a Warpstar.

In his second form Nightmare attacks Kirby by shooting stars at him, ramming into him, and using his tornado-like core to drill into him. He takes fewer hits to defeat then in his first form, but can only damaged by hitting his weak spot, the accumulation of darkness at his core, is usually protected by his impenetrable cloak. He reveals his weak spot whenever he attacks Kirby. After Kirby lands the finishing blow, Nightmare's body explodes, leaving a small crater in the moon, creating the classic effect seen on many cartoons and video games, supposing that this was Kirby's doing...

In the Anime
Likely because the Kirby anime was meant coincide with the release of Nightmare in Dreamland, Nightmare is the main villain in Kirby's anime series, despite actually appearing in only nine episodes (the whole series had 100). In a contrast to his fairly nonthreatening goal of simply spreading bad dreams in the game, Nightmare's goal is to conquer the universe. He's responsible for the creation of Nightmare Enterprises (known as Holy NightMare Co. in Japan) He creates and sells hordes of monsters that Kirby often has to fight. It's implied that the monsters eventually turn on the customers as well. The money he makes from it always goes to his conquest goals. There was a time when the Star Warriors and Galaxy Soldier Armystood in his way, but his army of monsters wiped them all out except Meta Knight, Kit Cosmos, Sir Arthur,Sir Falspar, Sir Dragato, and Sir Noisurat.

It's mentioned by Kabu that Nightmare created one monster that didn't obey him, though who it isn't ever stated. This is heavily implied to be Kirby, but it's possible that it might also be Meta Knight, as Kirby wasn't alive while the great war was going on.

Besides being able to create powerful monsters, Nightmare is also able to manipulate other peoples' minds, and even brainwash them. Like in the games, he is also impossible to hurt without the use of the Star Rod. Nightmare resides deep within his fortress, the Destrayer, for the majority of the show, creating monsters.

Nightmare rarely interacts with anyone and spends his time alone. Occasionally Nightmare speaks to Customer Service concerning their business, but mainly exists as a figurehead of the company.

Throughout the series, Nightmare is seen simply watching Kirby and Dreamland, and never seems to take Kirby for a threat. He constantly watches Kirby fight his monsters that he sells to King Dedede. One of the few notable actions was when he sped up the rate of an asteroid that was heading for Dreamland, which he seemed to mostly just do for his own amusement, as well putting money in his pockets from his best customer (and sucker) King Dedede.

Towards the finale Nightmare seems to decide to end his amusement with Kirby and sends some of his Destroya ships to kill him, but this also fails. Nightmare responds by sending another six, but these are destroyed by Meta Knight's battleship the Halberd. Even when the Halberd heads towards the Destrayer, Nightmare still doesn't take the one ship for a threat and attempts to stop with one last monster called Heavy Lobster. Even that monster failed, it proved nothing compared the defenses of the Destrayer, which the Halberd only just barely managed get past with help from the other Galaxy Soldiers and Star Warrior who each hijacked a Destroya. Despite that, once the Halberd entered and confronted Nightmare, it proved unable to do a thing against him and his fortress' defenses soon nearly crippled the ship. During this time Nightmare appears as a giant dwarfing the Halberd, though considering this form didn't do anything it's likely it wasn't real. Nightmare then kidnapped Tiff(Fumu) to lure Kirby into a fight with him. As Fire Kirby, Kirby tried to attack him but his fire breath had no effect. Nightmare then entered Kirby's mind to torture him before finishing him off, but Tiff, who was also in there, tossed Kirby a dream version of the Warp Star to Kirby, which he swallowed to gain the Star Rod ability- the one thing that could damage Nightmare. Kirby harnessed the power of the Star Rod and used it to destroy Nightmare.

Nightmare was also the real villain in Kirby of the Stars Pilot and the one who sends all the monsters at Kirby. In the end he is seen attacking Kirby and his friends with some kind of energy beam before Kirby wakes up and realizes that it only was only a nightmare.