I have seen "game items" listed on https://bloks.io/account/rektplebeian how are these items created, and issued?
Technically, these items are just numbers in
eosknightsio contract's tables which are stored in RAM on the blockchain.
However, as this is one of the popular games on EOS blockchain, the block explorer Bloks.io just went forward and made a custom page to display them.
The graphics are images from the game, reused by Bloks.io to mutual benefit of all affected parties.
The items are created and issued when you play the game, by the rules defined by the game contract. Its source is available on Github.