Implement any blockchain technology of your choice to qualify. But remember: your game can also participate by aligning its gameplay, visuals, or any other aspect of the entry with any NFT collection, blockchain platform, crypto tool, or web3 service.
Resources: Arcadians lore and assets, Game7 knowledge base, NEAR SDK.js. See last year's entries for example implementations. You can even host it on Flux for extra points.
Keep im mind that using any external assets will disqualify your entry from the overall results (the same way using provided libraries in the WebXR category does) unless you make it optional and download those extra elements only for this purpose. If you allow playing the entry without Decentralized features while not using anything outside the zip, then you will be able to be placed in the overall results.
That's it, good luck and have fun - unleash your creativity!