Valkyrio currently runs almost entirely on the blockchain, as opposed to centralized games running on their own servers.
Having all gameplay done on-chain provides a level of trust not commonly found in traditional video games, and allows all users to verify the code that runs the game, as well as all interactions happening on the game's smart contracts.
Valkyrio has a 99.99% uptime on their SLA with Netlify, and ensures smooth production and deployment of any features pushed to the website, as well as the usability of the website for all players.
DDOS attacks can disrupt marketplace and leaderboard data, but being on the blockchain ensures that assets are always safe and the game is always playable.
Off-chain refers to traditional games where gameplay code is executed on the developer's own servers. Such games are liable to DDOS attacks since all the game code is running on one central location.
Valkyrio, being on-chain, has a distinct advantage in that the website isn't necessary to play the game. Assuming the player knows how to interact with the blockchain, they can play entirely on the smart contracts by calling the appropriate functions and supplying the necessary data on the BscScan contract pages.