While the main crew is being beaten, Luffy is in the Thriller Bark forest. He meets a group of victims who have had their shadows stolen by Moria. They reveal a secret: if a person has a strong enough spirit, they can "host" the shadows of others to temporarily gain their skills and strength.
: His body swells into a massive, blue-skinned powerhouse. He isn't just a brawler anymore; because one of the shadows belonged to a master swordsman, Luffy suddenly becomes an expert with a blade. One Piece (Dub) Episode 370
: Luffy is stuffed with 100 shadows . Most people would pass out or die after two or three, but Luffy’s legendary willpower allows him to hold all 100. While the main crew is being beaten, Luffy
Here is an interesting breakdown of the story as it unfolds in the English dub: : His body swells into a massive, blue-skinned powerhouse