1. Go to Eumi island by through LiLyCove -> go to Park and receive the quest.
2. Return to Mauville city -> go to New Mauville, meet 2 people at the entrance -> talk to them
3. Go to LilyCove -> go to the Lighthouse on the right u will see the Phantom ship -> Defeat the leader and get the PART
(If u stuck by the Pirates try go around the lighhouse untill u see "Let take a break")
4. Return to New mauville and give the Part to Watson
Then u can go to the Park on Eumi island.
Finally ! Enjoy hunting ~~
P.s : i dont remember clearly the name of the map or the NPC