A Cryptokitties clone script is a software code structure built on the Ethereum blockchain. It is designed to allow customized development of a dApp game where players can collect, breed or exchange some kind of virtual characters. The game allows players to level up their virtual characters, breed some rare characters, use these to level up their game or sell these characters to other players in the marketplace.
As the dApp games core is already designed, it requires the blockchain dApps development team a week or so to customize and launch a game that is as capable as Cryptokitties.
Source: https://www.antiersolutions.com/how-to-build-a-dapp-game-like-cryptokitties/