Slay the Spire 2 — Lantern Key Guide
The Lantern Key is a two-part quest chain that starts in Act 1 and pays off in Act 3. Get it right and you unlock one of the strongest relics in the game. Here's everything you need to know.
Quick Answer
Fight the Mysterious Knight in Act 1 to get the key. In Act 3, use it to free Repy (not open the chest) for the History Course relic — it plays a free copy of your last card at the start of every turn. It's one of the best relics in STS2.
Step 1 — Getting the Lantern Key (Act 1)
In Act 1, you may encounter the Mysterious Knight event in a ? room. You find a faintly glowing key, and a heavily armored knight demands you return it.
You have two choices:
Hand it back
Receive 100 gold. The quest chain ends here — no Act 3 payoff.
Fight the knight ✓
Defeat the knight and keep the Lantern Key. The quest chain continues.
Always fight the knight. The History Course relic is worth far more than 100 gold.
The knight attacks constantly, so don't enter the fight at critically low HP. Otherwise, the fight is manageable at any point in Act 1.
Between Acts — The Key in Your Deck
After obtaining the Lantern Key, it sits in your deck as an unplayable card — similar to a curse. It won't actively hurt you, but it occupies a draw slot until you use it in Act 3.
The key is run-specific. If you die before reaching Act 3, it's lost with the run.
Step 2 — Using the Key (Act 3)
In the first half of Act 3, look for a ? room featuring a figure trapped in a cage — this is Repy, a war historian. This is where the Lantern Key activates.
You're given two choices for how to use the key:
Which Reward to Choose
Free Repy (History Course Relic)
RecommendedUse the Lantern Key to unlock the cage and free the war historian Repy.
Reward: History Course relic
At the start of your turn, plays a free copy of the last attack or skill you played on the previous turn.
Pros
- +Extremely powerful relic — effectively doubles your best card each turn
- +Works for every class and every build archetype
- +Unique relic not available from any other source
- +Scales with card upgrades — the copy benefits from the upgraded version
Cons
- −Only one relic (vs two from the chest)
- −Requires understanding which card to play last each turn
Open the Chest
Use the Lantern Key to unlock a chest instead of freeing Repy.
Reward: 2 random relics + 2 random potions
Four random items from the standard relic and potion pools.
Pros
- +Two relics instead of one
- +Two potions as a bonus
- +Higher item count overall
Cons
- −Random relics — could be weak or redundant
- −History Course is almost always stronger than two random relics
- −Potions are temporary; History Course lasts the entire run
History Course — Why It's So Strong
History Course plays a free copy of the last attack or skill you played on the previous turn, at the start of your next turn. This means:
Free
no energy cost for the copied card
Every Turn
triggers at the start of each combat turn
All Classes
works with any attack or skill
End your turn on a high-damage attack or a key skill, and History Course replays it for free next turn. With upgraded cards, the copy benefits from the upgraded version — making it scale with your deck quality.
Routing Tips
Quest Chain Summary
| Step | What Happens |
|---|---|
| Act 1 — ? Room | Mysterious Knight event appears. Fight the knight to obtain the Lantern Key. |
| Acts 1–2 | Lantern Key sits in your deck as an unplayable card. Survive to Act 3. |
| Act 3 — First Half | Find the caged character (Repy) in a ? room. Use the key to free Repy or open a chest. |
| Reward (Recommended) | Free Repy → receive the History Course relic. |
Frequently Asked Questions
What does the Lantern Key do in Slay the Spire 2?
The Lantern Key is a run-specific quest item obtained from the Mysterious Knight event in Act 1. It unlocks a special event in Act 3 where you choose between freeing a caged character (Repy) for the History Course relic, or opening a chest for 2 random relics and 2 potions.
Where do you find the Lantern Key?
The Lantern Key comes from the Mysterious Knight event — a ? room encounter in Act 1. A knight asks you to hand back a glowing key you found. You can give it back for 100 gold, or fight the knight to keep the Lantern Key. Fight the knight.
Is the Lantern Key worth fighting for?
Yes. The 100 gold from handing it back is decent, but the History Course relic (from the Act 3 payoff) is one of the strongest relics in the game. The knight fight is manageable — just don't enter it at critically low HP.
Where do you use the Lantern Key in Act 3?
In the first half of Act 3, at a ? tile event featuring a figure trapped in a cage (Repy, the war historian). Route toward early Act 3 unknown rooms to find it.
What is the History Course relic?
History Course is the reward for freeing Repy. At the start of your turn, it plays a free copy of the last attack or skill you played on the previous turn. This effectively doubles your most powerful card every turn — it's one of the strongest relics in STS2.
Should I free Repy or open the chest?
Free Repy. History Course is almost always stronger than two random relics. The only exception is if you already have a very weak deck with no good cards to copy — but even then, History Course scales with whatever you build toward.
Does the Lantern Key work like the keys in STS1?
No. The Lantern Key is completely different from the Ruby, Emerald, and Sapphire Keys in the original Slay the Spire. Those keys unlocked Act 4. The Lantern Key is a single-run quest item that changes one Act 3 event outcome.
What happens if I never find the Repy event in Act 3?
If you reach Act 3 but never encounter the caged character ? event, the Lantern Key goes unused. Route toward early Act 3 ? rooms to maximize your chances of triggering it.
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