A valuable but pricey consumable item - if you get killed with a phoenix feather in your inventory, it will automatically use itself to revive you at half health, giving you a few seconds of invulnerability in the process. The phoenix feather has a maximum stack size of 1. This item is really useful, especially when fighting bosses.
Phoenix feathers can be rarely found in dungeon chests and they can be crafted.
Crafting
You need a Feather, four Ghast tears and four Blaze powder to craft a Phoenix Feather.