Magic Cuffs

What comes back is tied to the raw incoming hit, before your defense trims it. A heavily armored player takes a big attack, loses almost no health, and still collects the full refund. That inverts the usual relationship between armor and casting: the tankier you are, the harder this accessory works.

The intended trick is building a damage source into your arena. A short row of spikes you can bump into refills you on demand, and unlike a potion it never triggers mana sickness, so your damage does not sag afterward. Bring something that stops bleeding first, since spikes cause it. Lava under an obsidian rose does the same job. Weak enemy projectiles work too, which is why this is unexpectedly good against the Wall of Flesh and the Destroyer, both of which pepper you constantly.

The whole approach depends on out-healing what you are doing to yourself. Jungle armor is the pre-hardmode pick for its defense. Later on, Spectre's lifesteal or Valhalla Knight's regeneration turn the self-damage loop into something you can hold indefinitely.

The recipe wants a Band of Starpower, which normally only comes out of corruption orbs. In a crimson world you either stand in a graveyard and combine a panic necklace with a mana crystal, or wait for hardmode, seed a patch of corruption using seeds from the Dryad and fish the crates out of it.