What does the Lantern Key do? Delayed rewards aren't always worth it in Slay the Spire 2 - often they give you some money, or sometimes a card - but when we say that the Lantern Key is worth going for, we really mean it. The prerequisites to obtaining the reward are tough, but we have found it to be an absolute game-changer every time we earned it. It doesn't matter which Slay the Spire 2 character you're playing as; the Lantern Key is an absolute must. While things like the Byrdonis Egg can add a little oomph to your damage output, the reward from the Lantern Key quest is a relic that can add a whole new dimension to your attack. Here's how to get the Slay the Spire 2 Lantern Key and what its eventual rewards are.