Nightmare (eNeMeE in the Kirby anime) is a final boss character and major character in the Kirby series. His goal is to spread dark nightmares and influences throughout the galaxy with his army of monsters. He first appeared in Kirby's Adventure and its remake Kirby: Nightmare in Dreamland as the final boss.
Nightmare appears as a Assist Trophy. When he is summoned, he will appear in his Power Orb form and fly off the screen, then his image will be shown in the background as the screen goes completely dark. Even the characters' indicators will be blocked, making the players completely unable to see. Even the CPUs will be programmed to be confused.
This ball of nightmare came from the Fountain of Dreams, taking nightmares to all of Dream Land. King Dedede sealed it away by shattering the Star Rod, but it was revived when the Star Rod was restored by Kirby. In Smash Bros., it hides the stage and the other fighters in pure darkness.