Slay the Spire 2 Lantern Key — Event, Choices and History Course Relic

The Lantern Key is Slay the Spire 2's quest-item chain: a two-act story that starts with a glowing key guarded by a hostile stranger and ends with a choice between one of the best relic pickups in the game and a pile of loose loot. Here is the full chain, verified option by option.

Step 1: The Lantern Key event (Act 2, the Hive)

The event appears in the Hive (Act 2) and is a combat event. You stumble on a faintly glowing key — and on its previous owner, who does not want to hand it over.

• Return the Key → gain 100 Gold. The stranger thanks you and the chain ends.
• Keep the Key → you fight the Mysterious Knight for the Lantern Key card.

Fighting the Knight is a normal combat encounter: it drops standard combat rewards in addition to the key, and it counts for on-combat-kill effects. The Knight hits hard — 101 HP (108 on high Ascension) and it opens the fight pre-buffed with Strength — so don't take this fight with a half-built deck. Win, and the Lantern Key joins your deck: an unplayable Colorless Quest card that reads "Unlocks a special event in the next Act."

Step 2: War Historian, Repy (Act 3, the Glory)

Once you hold the key, every question-mark room in Act 3 becomes the War Historian, Repy event — an academic trapped in a hanging cage next to a treasure chest. You choose one of two options, and either way the key is spent:

• Unlock the Cage → lose the Lantern Key, obtain the History Course relic.
• Unlock the Chest → lose the Lantern Key, procure 2 random potions and 2 random relics.

Because Act 3's ?-nodes all collapse into this event while you hold the key, carrying it changes your entire Act 3 routing — you are effectively choosing your reward the moment you leave Act 2 with the key.

Which reward should you take?

History Course ("At the start of your turn, play a copy of your last played Attack") is the pick for most decks:

• It turns your biggest attack into a free recast every single turn — doubling damage on finishers or re-firing setup attacks without spending a card.
• X-cost attacks copy at your current energy without paying it.
• The copy vanishes after resolving, so it never bloats your draw pile.

The chest's 2 potions + 2 relics is immediate value and never bad — but two random relics rarely match a relic that doubles your best card, every turn, for the rest of the run.

The key occupies a deck slot

Between events, the Lantern Key sits in your deck as an unplayable Quest card — a dead draw until Act 3, and if it is removed from your deck the Repy event stops appearing. One dead draw across an act is a fair price for History Course, but it is worth remembering when a card-removal event looks tempting.

Keep reading:

• Multiple Lantern Keys — the Stacked-Key Secret
• Act 1 Events Guide
• Map Room Types and Route Planning