Gensokyo/Divine Iron Ring

The Divine Iron Ring is a Hardmode ranged weapon that does not require any ammunition. It throws rings than can pierce an unlimited amount of enemies, and will keep bouncing off of walls. However, a player can have only three rings active at once. After four seconds, they will return to their owner, now passing through all tiles. Alternatively, they can be manually recalled using Right Click.

The Divine Iron Ring can be bought at the Curio Trader after defeating all Tier 6 Bosses. Alternatively, defeating any Tier 7 Boss will also suffice to unlock the weapon.

Trivia

 * The Divine Iron Rings are a reference to Suwako Moriya's spell card Divine Tool "Moriya's Iron Ring".