Specifically, I mean that game items could be attained through POW. An example would be crafting. Other items could be committed to this crafting operation as ingredients (referenced as preimage tags). The POW (NIP-13) yields a new item that required other items and energy to produce. Since its a game, you can require events to be published to the game's dedicated relay. This allows the game clients to check for double spends on ingredients. I'm working on a game that uses a system like this. The event ID of the item must contain leading zeroes, and the digits after the zeroes must match a certain bit suffix to yield a particular item. The game functions as an interpretation mechanism for POW. Game items could also be purchased for sats. Crafting and buying are different things.