In these smart contracts what it is going to do is upgrading star level for the NFT. In Ecio.space we have 5-level star NFT and it affect limit of the in-game level. As you can see the conditions below the in-game maximum level is 150.
Another condition for the upgrade, user need to have required materials to upgrade their NFTs' star. For example If you user has Rare Space Warrior, user can use Common or Rare materials.
Last condition, numbers of materials affect success rate. To upgrade to 2-Star NFT you need to have 2 Space Warrios to get 100% success rate.