Talk:Rusted Key/@comment-28232474-20190901051336

I cannot confirm, but I suspect the rarity of the item (and in fact, the identity of the item) in the Rusty Lockbox is determined when the level begins, and will not change if keys are acquired within the level. So, if you start a level with five keys, and then find four more keys in that level before opening the box, it won't increase your chances of finding a rarer item until you go to the next level. You might as well open the box as soon as you find it, instead of hunting for more keys to try for a rarer item. The reason I think this is because the levels are created from a seed, which encodes information that determines which items are in each chest on the level, as can be seen when performing a Prismatic Trial (all chests are always in the same location and always contain the same item as long as the level seed is the same).