AFK Pets and more/Kappa's Backpack

The Kappa's Backpack is a Hardmode wing-type accessory obtained from Martian Saucers. When the player has less than 40% of their health, a Soul Heart pickup will be generated on the player's position every ~3 seconds, healing them by 20 health points.

Trivia

 * This item is a reference to the backpacks commonly used by Kappas, specifically, the Kappas from the Touhou series, as the Japanese Mythology counterparts don't use any accessories and have a much more threatening appearance.