- "I am the evil part of your mind. You can't beat me. Because you are the one who forced me into being..."
- — Ness's Nightmare
Ness's Nightmare is a boss in EarthBound. It is encountered during Ness's venture in the Sea of Eden within Magicant, and is the representation of the evil in Ness's mind. As such, when Ness's Nightmare is defeated, Ness destroys all of the evil, fears, and doubts that were within him, allowing him to absorb the true power of the eight Your Sanctuary locations. The field sprite for Ness's Nightmare is identical to that of Evil Mani Mani, though the relationship between the two, if any, is uncertain. It is possible that Ness's mind chose the Mani Mani Statue as a known symbol of evil. Also, it is also possible that the trait of the Mani Mani Statue bringing out the evil in people may have influenced Ness's inner turmoils to conjoin into the form of the Mani Mani Statue.During the battle, as the representation of Ness's evil, Ness's Nightmare's attacks are all the same PSI attacks Ness can use; this includes various levels of PSI Rockin and PSI Flash (via a glorious light), PSI Lifeup and Shield β.
- When the Eraser Eraser is used on the statue outside of battle, a text box will come up saying, "It looks like some sort of primitive human statue if you look at it from the right angle... But it definitely doesn't look like an eraser... does it?" Apparently, the same speech can be found by using the Eraser Eraser on the Evil Mani Mani in Moonside, despite the fact that the Eraser Eraser is not obtainable at that point in the game. Also, the speech occurs if you use the Pencil Eraser on the Evil Mani Mani or Ness's Nightmare.
- The fight background of Ness's Nightmare is very similar to the Evil Mani Mani's battle background and the Masked Man's in Mother 3 when he is fought for the last time.
- Ness's Nightmare is the last of the five bosses who has the music "Otherworldly Foe" for its battle theme, the other four being Starman Junior, Mr. Carpainter, Evil Mani Mani, and Clumsy Robot.
- In Mother 2, Ness's Nightmare is actually called something along the lines of "Ness's Devil" or "Ness's Demon". However, Nintendo's American division changed this to "Nightmare" in order to avoid religious references in the game.
- It seems that Ness's Nightmare has a golden battle sprite, even though its field sprite appears to be some sort of purple. The Evil Mani-Mani has a golden field sprite, but a purple battle sprite. Whether this was a mistake by the developers or meant to be is unknown.