Instructions
Complete the game up to "Section 6: Sinister Slug Defeated." Walk over to Karen and chat with her. Listen to her tell you that the Flying Dutchman has appeared and that you should find him.
Go to the bus stop and activate your super strength. Throw the box at the wall and super jump from it. Make your way over the canopy platforms. Go down the path and enter Rock Bottom.
Go straight ahead until you see the Flying Dutchman. Talk to him and accept the missions he gives you. Complete the five missions he gives you and return to him to finish the Flying Dutchman section of the game.