Steel Fly

Steel Fly is a unique familiar summoned by the Steel Ball weapon item, which can be used once per battle to deploy it. What makes Steel Fly exceptional is its complete invulnerability to standard damage and status effects — only instant-death abilities such as Daddy Shark's consumption can remove it from play. In combat, it targets bleeding enemies preferentially and gains bonus actions for each bleeding unit on the battlefield, giving it strong synergy with bleed-focused builds.