Mario and Luigi are walking around Delfino Plaza looking for something to do.
Pianta: AAAAAAHHH!! It's horrible!
Following the sudden scream, the Brothers go to the docks. Suddenly, before their eyes, they see a giant glob of graffiti on the nearby dock.
Mario: Luigi, are you thinking what I'm thinking?
Luigi: Yeah!
Mario and Luigi spray the center of the glob and reveal a Piranha. After spraying its mouth three times, it disappears.
Luigi: What the?
Mario: The sludge didn't disappear?
FLUDD2: Mario, Luigi, there's probably a second Piranha in that sludge.
Mario: So it seems...
Mario and Luigi spray the center, reveal a second Piranha, spray its mouth three times, and defeat it. The sludge disappears and a boathouse appears at the end of the dock. Beside it is-
Mario: YOU!!!
Shadow Mario paints a sloppy M on the
boathouse wall and jumps in. Mario and Luigi spray the M and pursue the
imposter into the graffiti.