stacking rusted keys

[Syrius]

So, now that rusted keys changed, is it useless to stack them ?
I tried getting 2 keys before the next level, but then I only saw one chest, and I could open it one time only, so I had an extra key for the next level, but does that mean it's useless to stack more than the number of levels left to do ?

[Lunacy]

Yea a 2nd key just means you'll get to find 2 lockboxes, 1 in each next level (and multiple lockboxes if multi, 1 for each player who has a key), until they're consumed. It's better for early game since you're basically turning a white into a green, since its old purpose was pretty much only useful in those really long 2 hour runs.