Clown

Nothing summons one. It is an uncommon hardmode spawn that only appears while a blood moon is running, so farming it means farming blood moons, which in practice means saving a Bloody Tear rather than waiting on the calendar. Only one can be alive in the world at a time, so a screen packed with blood moon enemies still holds at most a single clown. A Lifeform Analyzer picks it out of that crowd. Its banner arrives at half the usual kill count, which softens the rarity a little.

Two kinds, and they behave differently. The thrown ones arc, bounce off whatever they land on, and detonate when you come close or when the fuse burns out, so a bomb that missed is still a timer sitting on your floor. The blast covers a wide square. The other kind walks after you and explodes on arrival, which punishes standing still to fight. Neither breaks terrain, so your arena survives, but a bad bounce in a small room ends you outright. It does not need to see you to throw, so ducking behind a wall achieves nothing.

Hitting it resets its throw timer, so sustained damage keeps a bomb from ever leaving its hands and a fast weapon locks it down completely. Since only one exists at a time, that lock is realistic even in the middle of a blood moon. If you cannot close the distance, keep moving sideways, because the bombs land where you were rather than where you are going. It is not fast enough to punish a retreat. The explosives glow, which is your warning about where the last throw came down.

In Celebration Mk 10 worlds the thrown bombs stop detonating on proximity and have to actually touch you, which makes the whole encounter far more forgiving. Remix worlds swap its signature weapon drop for a Chain Knife.

The first one that dies in a world permanently unlocks the Clown Hat and the rest of the outfit at the Clothier. Past that it is the only source of the KO Cannon, a reasonable route to the Bananarang, and one of the blood moon enemies that can hand you a Bloody Tear so you can arrange the next one yourself.