While the diamonds found in levels power the game’s overarching economy, you’ll have to rescue most of the lobby shopkeepers before you can spend your ice. Many vendors are found trapped in golden cages, and will direct you to dig for or purchase the matching key to release them. That done, they’ll appear back in the lobby, a few ready to unlock new items or remove them from the potential pool, but the majority offering ways to train against enemies. The most useful shop keeper, however, is held in a glass cage, and he returns meaning to diamonds by letting you buy items to start runs with. Since his key can only be found in secret rooms and shatters when you take a hit, great care and skill are needed before you can dictate your starting weapon.