Don't Dread on Me

The Dreadnautilus is a hardmode Blood Moon fishing 'catch' - cast with any bait into water during a Blood Moon and it can take the line instead of a fish (Chum Caster and higher fishing power help the odds). It's a genuinely nasty fight for its tier: relentless charges and blood-spike sprays, so treat it like a mini Duke - open sky arena, good wings, sustained DPS. The Sanguine Staff from its blood-moon stablemates makes a fine consolation while you farm.