From Guild Wars 2 Wiki
Hint: Use the Gloominator to capture the darkness of the dark room in the Obsidian Sanctum jumping puzzle in The Mists.
— In-game description
- Use your Gloominator inside the dark room of the Obsidian Sanctum jumping puzzle. You don't have to go in very far; in fact, you can capture before you even get to the bottom of the first set of stairs.