The combination of a $2,000+ chase card, strong alternate art leaders like Perona and Reiju, and enduring competitive relevance keeps demand high for both sealed boxes and singles
You might build your build your deck around these cards or simply use them to enhance the power of an ex card, but either way, they will undeniably elevate your game
Empty the Warrens becomes more effective the more cheap spells you have to cast, but it's pretty stellar with even one storm copy
In fact, thanks to giving you mana right away, there will be turns where she essentially costs just two mana
When properly utilized, these cards greatly place the odds in their owner's favor, making the game less about strategy and more about who draws their powerhouse cards first
It fits my definition of potentially making more mana than it costs, but its dependent on your opponents discarding a specific type of card