Mario and Luigi go back to Noki Bay in Episode 6.
Mario: We just get this 100-coin Shine and we leave this place that reminds me of Jolly Roger Bay!
Luigi: Right!
Mario goes to collect the coins hidden in the walls.
Luigi goes to collect the coin on the water with the mudboat.
Luigi: It's mudboat time!
Luigi uses his FLUDD2 to move around.
Mario uses his FLUDD to spray the walls.
Luigi:Yes! Just 40 more coins to go!
Mario: Yes! Just 39 more coins to go!
Luigi follows the path of coins carefully until he crashes!
Luigi: Great! Now I have to go all the way back!
Luigi decides not to go back.
Luigi: Maybe I can hop for the coins!
Luigi swims along the coin line and colects 50 coins.
Luigi: Yeah!
Mario has to find eight more coins, which are in the secret cave.
Mario: I think I'll go to the secret cave.
Mario enters the secret cave and Luigi falls with him.
Mario: Where did you come from?
Luigi: I saw you so I came along!
Mario and Luigi put their coins together and the Shine appears on the tip of a tall tower.
Luigi: I'm-a tired of climbing!
Mario switches to Rocket Nozzle and makes his way to the Shine twenty minutes later.
Mario: Wahha!
Luigi: On to the next world!