Risk of Rain 2 Rusted Key and Rusted Chest Explained
Risk of Rain 2 has an abundance of different items and equipment for players to find and use randomly around the hostile world.
Players acquire these items either through killing a boss or by finding them randomly in chests and boxes around each level, but one box, in particular, doesn't seem to want to open at first glance. We are, of course, talking about the Rusted Chest that has a habit of appearing once in a blue moon in various levels and maps.
This chest can only be opened through the item "Rusted Key" which is sadly locked when you first play the game through a somewhat difficult challenge. This challenge (or achievement depending on who you ask) wants you to kill a teleporter boss in under 15 seconds, which isn't as easy as it sounds. Honestly, the only way to go about doing this challenge is to either play MUL-T or the Engineer solo and just spam tons of damage at the boss or wait until later on in a run when you have so many items that you shred through anything within seconds.
Once you unlock the item, you'll need to start a new run and hope to find a Rusted Key to open Rusted Chests across the map. Granted, there is no guarantee a key will spawn and even if it does if you will find a rare Rusted Chest in the first place, but these chests always seem to pack high-quality loot in them when you do finally put two and two together.
You only need a single Rusted Key to open up every Rusted Chest in a run, so sadly getting two or more is kind of useless in the long-run. If you can, you should try to recycle some of the spare Rusted Keys into new items through a 3D printer or another item.