[2] Infernax is a 2D Metroidvania game set in a dark fantasy world where the player controls the young Duke Alcedor, while the second player controls Cervul the Squire;[3] both of them find their village overrun by a sect of satanists and a lot of monsters upon returning from the Crusades.

[4] Gold is used to buy upgrades for equipment, while earning enough experience points allows players to increase their health, mana (Alcedor only), or attack power.

However, the ancient tome known as the Necronomicon, a book written by a madman rumored to hold great power, has been brought to Upel around a year before Alcedor’s return.

As a result, hordes of monsters have been ravaging the duchy, with Alcedor having to help defend the town of Darsov from an attack upon his return.

After tracking down and slaying the monster outside the Urzon Citadel, Alcedor finds that the way inside is blocked by a magical seal.

Father Henry, a priest from Darsov, explains that Alcedor must track down and destroy five crystal orbs scattered across Upel that keep the seal in place by killing the elder demons that hold them.

Once all five crystal orbs have been destroyed, the Urzon Citadel will be unlocked, allowing Alcedor to enter and encounter a powerful demon known as Belphegor.

[15] An update to the game, called Deux or Die, was released on April 5, 2023, in which a second player can control Cervul the Squire, who chooses to be loyal to Alcedor, right or wrong.

The team also drew inspiration from the heavy metal genre, influenced by bands such as Mercyful Fate to "fit the feeling we wanted for the game".

Gipp felt that familiarity let Infernax down, but wrote that it was done in a way that "you won't really care unless you're desperate for a completely fresh experience".