Rusted Key

The Rusted Key is an unlockable common item in Risk of Rain 2. When a player has this item, a Rusty Lockbox spawns somewhere in the next level. The Box contains an Item, the rarity of which is determined by the amount of Rusted Keys all the players have when any one of them opens a box.

The Rusty Lockbox is quite small and easy to miss, but it's dark color and rectangular shape usually make it stand out. It can be opened by players who don't have a key. Opening the box costs nothing, and will trigger Bundle of Fireworks.

The Challenge Keyed Up unlocks this item.