Illuvium is an open-world fantasy battle game built on the Ethereum blockchain. Often touted as the first AAA game on Ethereum, Illuvium aims to provide entertainment for both casual gamers and hardcore DeFi fans through a range of collecting and trading features. The world of Illuvium is inhabited by creatures known as Illuvials, which players can capture by defeating them in battle and nursing them back to health. Once captured, Illuvials become a loyal part of the player's collection and can be used when battling other adventurers as part of Illuvium's auto battler gameplay. The game combines elements of open-world exploration and PvP battles. Players can spend their time exploring the vast game world or building up their team of powerful beasts. Illuvium has been in development since 2020 and is being built by a global team of over 40 individuals, including the co-founders Kieran Warwick, a serial entrepreneur and early cryptocurrency adopter, and Aaron Warwick, an experienced game designer who are brothers (and incidentally, also the brothers of Kain Warwick, the co-founder of DeFi platform Synthetix).

While Illuvium incorporates blockchain-based elements, it is more like a traditional video game. It can be accessed through a downloadable desktop app and has a range of supporting DeFi applications, including a yield farm and decentralized exchange. In the game, players explore the Illuvium landscape, battling Illuvials and other players, participating in quests and daily challenges, and engaging in its communal storyline. Throughout their journey, they collect Illuvials, which have various characteristics that determine their rarity, utility, and desirability. The most important attributes of Illuvials are their class and affinity, but each Illuvial also possesses a large number of additional attributes that contribute to its combat strength. Illuvials become stronger with victories, can be enhanced with in-game items, and can be upgraded into a special "ascended" form that benefits from two affinities simultaneously.

Each Illuvial is represented by a unique non-fungible token (NFT) and can be freely traded on external exchange platforms and the gas-free IlluviDEX. They can also be fused to create more powerful forms and are available in normal, holographic, and dark holographic variants, with the latter being considerably more scarce. Illuvium features a unique yield farming reward system where all ILV rewards earned through the yield farm are locked for a period of one year before they can be withdrawn. However, stakers have the option to skip the unlock timer by converting their ILV rewards to a secondary in-game-only asset known as sILV. By claiming their rewards as sILV, users receive the USD equivalent of sILV and can spend their rewards early to purchase in-game items. sILV cannot be withdrawn from the game and is not represented by a blockchain-based asset.