In Hephaestus Protocol, players pick one of over 50 playable heroes, and try to survive escalating waves of enemies while traversing an infinite, procedurally generated, map. The world draws on mythological pantheons, traditional fantasy, and historical elements. The core loop is pure Bullet Heaven adrenaline: move, dodge, and let players auto-firing arsenal do the work while they level up, accumulate catalysts, and decide which weapons to evolve. The primary innovation is the weapon combo system; items can be combined together into hybrid armaments that merge their stats, elemental affinities, attack patterns, and sprites, giving each run a distinct, build-defining identity.