Infernal Arms

Weapons are your main mode of attack. Initially, you only have the Stygian Blade available, but additional weapons can be unlocked by spending Chthonic Keys in the Arsenal Room. Unlocking all the weapons requires a total of 24 Chthonic Keys. They can be upgraded during a run with a Daedalus Hammer.

Each weapon has a number of "Aspects" that can be unlocked using Titan Blood. Aspects become available one run after the Rail has been unlocked and the player has collected at least one Titan Blood.

The infernal arms are the weapons the Olympians used to defeat the Titans. They abound them afterwards, but the arms are supposedly the strongest or some of the strongest weapons that exist in the universe which is why they are supposed to be locked away. Why exactly they appear in the courtyard, is unknown. Because of their history with titan blood they both react to it when it is collected and seem to have developed some form of consciousness.