That sounds like a great use-case for soulbound tokens! You can do this with Heymint Launchpad. The upgradable aspect is easiest to implement by updating the token metadata and images as users complete tasks or sessions. This way you actually don't need to make any changes on the blockchain whenever you upgrade a token. It's enough to update the metadata file and image. ​ Metadata files and images are most commonly stored in IPFS, but for a use-case like this it probably makes more sense to store those files on your own servers. You can store them anywhere and use this option in Launchpad to provide the URL to the metadata files so that marketplaces like OpenSea will find them: ​ ​ If you decide to host metadata and images yourself then you only need to set this "token base URI" once. After that it's enough to simply change the metadata wherever you've stored it and refresh metadata on OpenSea, to see the changes to the token. This will appear as "evolving" tokens to the users. ​ One note of caution though: Hosting metadata and images on your own server is considered risky and some users might wonder why it's not stored in IPFS. The risk comes from the fact that your servers need to stay online for the marketplaces and wallets to be able to fetch metadata and images. If your servers ever go down (because of an unpaid bill, for example) then the tokens become empty shells with no attributes and no images. So if you decide to go this route, make sure that the hosting you choose is solid, has automatic backups and that you can commit to keeping it running for a long long time. ​ If you get to a point in the future where your metadata and images no longer are going to change any more, then it's possible to upload it to IPFS at that point. By updating the "token base URI" again to point to the IPFS location you'll secure the tokens for the future. At least as long as you keep paying services like Pinata for pinning the IPFS files.