To find the 2nd gem in Gloomy Manor, you need to follow these steps:

1. Leave the Mansion: Exit the mansion through the front door.
2. Go to the Yard: Once outside, head to the yard, which is located on the left side of the stairs leading up to the house.
3. Flash the Flower: Look for the second purple flower on the left side of the stairs. Flash Luigi’s light on this flower to reveal the gemstone.

By following these steps, you will be able to collect the second gemstone in Gloomy Manor.