Lantern Key in Slay The Spire 2: How to Get & Use It
What the Lantern Key does in Slay the Spire 2, how to get it from the Mysterious Knight in the Hive, and how to use it in the War Historian Repy event.
The Lantern Key in Slay the Spire 2 is a quest card from a combat event of the same name: you find a faintly glowing key in the Hive, choose to fight a Mysterious Knight for it instead of taking 100 gold, and the unplayable Lantern Key card then unlocks a special event — War Historian, Repy — in the next Act (Act 3).
What the Lantern Key Is
The Lantern Key appears as an Event found exclusively in the Hive. It's a combat-room-style event: you come upon the glowing key and pick it up, and its owner — a person who "looks like bad news" — immediately shows up: "Been looking all over for that key! Now if you don't mind..."
The key itself travels with you as the Lantern Key card, an unplayable card with a quest marker whose text reads: "Unlocks a special event in the next Act." It is not a relic and not something you play — it just sits in your deck as a pass to the Act 3 encounter.
How to Get the Lantern Key
At the event you have two choices:
| Option | Result |
|---|---|
| Return the Key | The stranger thanks you and rewards you handsomely: 100 Gold. |
| Keep the Key | The stranger turns menacing — "it seems like only one of you is making it out of here with the key" — and you enter combat against the Mysterious Knight for the Lantern Key card. |
Win the fight and the Lantern Key card is yours. The Mysterious Knight is a stronger version of the Flail Knight (from the Knight Gang encounter) with innate Strength and Plating. Its HP isn't listed in our sources (to be confirmed), but its move pattern is documented:
| Move | Effect |
|---|---|
| Ram (opening move) | Deals 15 damage (17 on Ascension 9+) |
| Flail | Deals 9 damage x2 (10 x2 on Ascension 9+) |
| Breaker | Gains 3 Strength |
After the opening Ram, it randomly picks Breaker (equal chance), Flail (double chance), or Ram (double chance), and never uses the same move twice in a row — so expect an early Ramp-into-Flail burst and plan your block for the second turn.
How to Use the Lantern Key
The Lantern Key card is spent in the War Historian, Repy event in Act 3. Since update v0.77.0, picking up the key guarantees that the first unknown room you enter in Act 3 is the War Historian, Repy event, so the pass always connects to its reward rather than leaving you to hunt for the room.
What exactly the event grants in exchange for the key isn't documented in our sources — to be confirmed. What the patch record does show is that the Repy encounter hands out meaningful extras: a History Course relic is attached to the Lantern Key event chain (adjusted in v0.59.0 so it no longer replays cards from two turns ago after a turn where you played nothing), and since v0.105.0 something special happens if you hold multiple Lantern Key cards — an interaction that deliberately doesn't apply in multiplayer, where duplicate Lantern Key bonuses from the Repy event are also disabled.
Which Option Should You Pick?
The event is a straight trade: 100 Gold now (enough to matter for an early shop purchase) versus a guaranteed Act 3 event pass. Our sources don't quantify the Repy event's payoff, so there's no documented "correct" answer — the choice is whether the immediate gold serves your current run better than an Act 3 hook you can't price yet.
The event has been polished steadily across Early Access: the Return reward was set to 100 Gold in v0.86.0, the event became combat-room-style in v0.94.0, a typo was fixed in v0.110.0, and a loading hitch on the event was reduced in v0.111.0.
Fighting the Mysterious Knight is a mid-run check, not a wall — for the fights that actually end runs, see our boss guide, and if you're deciding whether a 100-gold swing matters for your deck, the tips guide covers shop and gold priorities.