Abstract: A computer system operates an off-chain electronic game that includes in-game assets stored off of a blockchain. The computer system detects an occurrence of a progression event related to a particular in-game asset associated with a particular player. In response to the occurrence, the computer system increases an upgrade capacity of the particular in-game asset. The upgrade capacity controls a maximum number of attribute upgrades that can be applied to the particular in-game asset at a time. The computer system then permits or prevents application of attribute upgrades to the particular in-game asset based on the upgrade capacity. The computer system further permits or prevents application of attribute upgrades based on whether the attribute upgrades are being applied to other off-chain electronic games. An interoperability API is used to determine whether a given attribute upgrade is being used in another game.