From the Super Mario Wiki
Luigi has to capture all ghosts in a room in the shortest time he can. The order of the rooms and the amount and variety of ghosts are randomized every time Luigi does this mission. After clearing the sixth room, the mission is completed.
We have an...interesting situation. The Parascope is picking up mild paranormal signals in the manor. I'm sending you in to investigate.
When clearing the Gloomy Manor of ghosts, what E. Gadd will say to Luigi at the end of the mission differs depending how quickly Luigi completes it:
"That'll do, Luigi! You weren't exactly quick about it, but you caught 'em all. Anyhoo, let's bring you back!" (Time over 4 minutes)
"Excellent, Luigi! You got all of 'em! That was really fast! The very definition of posthaste! Heh heh... Let's bring you back!" (Time under 4 minutes)
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