The Darkblock API enables you to create and access Darkblock unlockable content and build products that enable your users to do the same.
For adding content to pre-existing NFTs (NFT upgrades) you can use the mintDarkblockUpgrade API directly.
Multiple NFTs can be upgraded at the same time by using the mintDarkblockUpgradeCollection API endpoint. Traits within collections can also be targeted.
If you want to create the darkblock first, and embed the Darkblock-ID in the NFT metadata you can use the mintDarkblock API.
With either the nftid or the txid the Darkblock API getDarkblockInfo endpoint can be used to retrieve darkblocks.
Next, creator and owner verification is easily established, using the getDarkblockCreator and getDarkblockOwner endpoints.