Similar Questions for How did Luffy Get His Scar from Yahoo AnswersQuestionAnswer
the wound was caused by a blow Akainu.
Chapter 1, Luffy cuts himself to show he is not scared of being hurt, so Shanks would take him out to sea. Didn't work, just gave Luffy the scar.
Hope this helps.
Well, if you read the manga, you will see that Zoro got to same island with Mihawk, Usopp got to the island with many plants, Nami got to some kind of weather country, Robin got to Dragon's forces, Franky got to Dr Vegapunk's lab, Chopper got to some island with people and bird fighting, Brook got to some country and started as rockstar, Sanji to Okama land, etc, hence the power ups