- "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 manifestation 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. 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 manifestation of Ness's evil (essentially a part of Ness), the Nightmare's attacks are all the same PSI attacks Ness can use; this includes various levels of PSI Rockin, 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?" The same speech can be found by using the Eraser Eraser on the Evil Mani Mani in Moonside, although this requires modifying the player's inventory using hacking programs.
- Similarly, using the Pencil Eraser on the Evil Mani Mani or Ness's Nightmare will result in the speech "How could you possibly think that looks like a Pencil"?.
- The background of the battle against Ness's Nightmare is very similar to the background of the Evil Mani Mani battle, as well as that of the final battle against the Masked Man in Mother 3.
- 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 intentional or a mistake by the developers is unknown.