Mario and Luigi were just standing on top of the Shine Gate as this segment begins. They were discussing the fact that they had cleared all episodes in every other level except Pianta Village, which is why they were up there. All that was left was Episodes 7 and 8, the 100-Coin Shine, and any other secret Shine.
Luigi: Well, Mario, it's-a time.
Mario: You-a said it, Luigi.
So Mario and Luigi entered Pianta Village, Episode 7. It was night, and standing before them was Shadow Mario!
Mario: This-a is going to-a be easy compared to those-a last few!
Mario sprayed Shadow Mario with FLUDD. Shadow Mario started to run, but just before Mario ran after him, FLUDD2 gave warning!
FLUDD2: Look out, Mario! He's leaving behind a lava trail!
Mario stopped just before he set foot in some lava goop.
Mario: I-a see he's-a learned a new-a move! Luigi, I'll-a chase that rascal, while you-a spray the ground free of-a lava!
So, Mario began to chase Shadow Mario, with Luigi following. Luigi sprayed the ground ahead of Mario, while Mario followed Shadow Mario while squirting at him. Eventually, Shadow Mario fell. Luigi sprayed the ground around the villain, while Mario walked up and interrogated.
Shadow Mario: You haven't heard the last of me! I'll have my revenge soon enough!
And so, Shadow Mario dematerialized, and left a Shine.
Luigi: Let's-a grab it together!
And so, the Mario Brothers grabbed the Shine simultaneously and did the Shine Dance.
Mario Bros: We-a did it! Onto the next-a Shine!
FLUDD2: You know, I wonder what Shadow Mario meant by 'revenge'.
But meanwhile, in Delphino Plaza....
The dam for the lake beside Corona Mountain, above Delphino Plaza, had burst open. The entire area was flooded in seconds. All the villagers had to swim to the rooftops for safety. The only character who could have committed this was a shadowy figure that we all know and hate.
Shadow Mario: Vengeance will be mine!