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The Seven Needles in Mother 3 are a major plot point, being mostly introduced in Chapter 7, although appearances of the Needles and vague mentions of them have occurred before then.
In Mother 3
The Dark Dragon protects the Nowhere Islands in its sleep with its unlimited powers, however, if the Dragon were to be ever awakened, its power would be too much for any human to control. To keep the Dark Dragon from waking up, the Seven Needles were created and placed all over the islands by the Magypsies's ancestors. A Needle exists for each of the Magypsies, and they all guard their respective Needles closely.
The only ones destined to pull the Needles is anyone who has learned PK Love, an extremely rare and exclusive ability. The chosen one's heart will be passed onto the Dark Dragon and obey them completely, regardless of if they are good or evil. If they have good intentions and a pure heart, the Dark Dragon will recreate the world and vanquish all evil. However, if one has wicked intentions and wishes to destroy the world, the Dark Dragon will obey without hesitation.
Lucas and the Masked Man are the only ones bearing the ability to pull the Seven Needles. While Lucas is pulling the Needles for good, the Masked Man lacks any intentions himself, being completely controlled by Porky, who intends to destroy everything.
"Seven Needles" Memo description
"Once all of the Needles are pulled, what will happen? The die is cast. There is no choice but to go on."
"Needle Locations" Memo description
"There are seven Needles in all. The Belly Button Needle is in Osohe Castle. The Heart Needle is in Murasaki Forest, near the factory. The Left Hand Needle is located on Snowcap Mountain, far to the northeast. The Right Hand Needle is located in the crater of a volcano to the far east of the highway. The Right Foot Needle is located on Tanetane Island south of Tazmily. The Left Foot Needle is in the temple of Chupichupyoi on Mt. Oriander. And the last Needle... No one knows where it is. Too bad."
- The second through fifth Needles, in reality, may be pulled in any order. However, the most common and linear order is as listed above.