In Luigi’s Mansion 2, gems cannot be collected at any time. Each gem is specifically located within a particular room or area of a mansion, and collecting them requires completing specific objectives and navigating through the game’s levels in a particular order.

1. Gloomy Manor Gems:
– Gems in Gloomy Manor are scattered throughout the mansion and can only be accessed as you progress through the levels. For example, the first gem is located in the Mudroom, which is accessible during the “Poltergust 5000” mission.

2. Haunted Towers Gems:
– Similarly, gems in Haunted Towers are found as you progress through the levels. Each gem location is tied to specific missions and areas, such as the first gem being in the Yard, which is accessible during the “Gear Up” mission.

3. Old Clockworks Gems:
– In Old Clockworks, gems are hidden in various rooms and can only be found by completing specific objectives. For instance, the first gem in Old Clockworks is located in the Clockworks Court and requires using the Strobulb to activate a bomb and then using the Dark-Light Device to uncover a chest with the gem inside.

4. Secret Mine and Treacherous Mansion Gems:
– The same principle applies to the other mansions: Secret Mine and Treacherous Mansion. Each gem is tied to specific missions and areas, and collecting them requires following the game’s progression and solving puzzles or completing tasks as they become available.

In summary, gems in Luigi’s Mansion 2 are not collectible at any time but must be found as you progress through the game’s levels and missions. The locations of the gems are carefully designed to be accessible only after completing specific objectives and navigating through the game’s world in a particular order.