Slay the Spire 2 Act 3 Boss Guide: Doormaker, Queen, and Test Subject

The Final Gate

Act 3 bosses are the last thing standing between you and a win. By Glory, your deck should be assembled and functional. There’s no time to patch holes. These fights test whether your run was built on a real plan or whether you’ve been coasting on decent card rewards and lucky relics.

All three bosses are dangerous, but they’re dangerous in different ways. Doormaker warps the game rules. Queen hits like a freight train. Test Subject adapts to your playstyle. You face one per run, chosen randomly.

Doormaker

Doormaker is the boss people complain about online, and honestly, I get it. This fight breaks the normal rules of Slay the Spire in ways that feel unfair until you understand what’s happening and build for it.

Doormaker’s mechanics target your deck’s functionality directly. It exhausts cards from your hand, prevents you from drawing, and increases card costs. If your deck depends on playing a high volume of cards or relies on specific combo pieces, Doormaker dismantles your strategy one piece at a time.

The fight has phases. Between phases, Doormaker alters the rules — sometimes limiting your draw, sometimes making cards cost more, sometimes removing cards from the fight entirely. Each phase escalates the restrictions.

General strategy: Play your strongest cards early, before Doormaker takes them away. Prioritize cards that provide lasting value (Powers, ongoing effects) over cards that need to be drawn and played repeatedly. Once a Power is in play, Doormaker can’t exhaust it. The fight rewards setting up your engine in the first 2-3 turns and then surviving on passive effects.

Relics matter more in this fight than almost any other. Relic effects can’t be exhausted or cost-increased. A strong relic loadout can carry you through phases where your hand is nearly non-functional.

Ironclad: Barricade and Body Slam is the gold standard. Once Barricade is in play, Block accumulates permanently — Doormaker can exhaust your block cards from hand, but it can’t remove the Block you’ve already built up. Demon Form is also excellent because Strength persists regardless of hand disruption. Get your Powers down early.

Exhaust synergies actually work against you here because Doormaker is already exhausting your cards. Don’t build around Feel No Pain or Dark Embrace against this boss — you’ll run out of cards faster than you want.

Silent: Wraith Form is your best card. Intangible reduces all damage to 1 for multiple turns, buying time even when your hand is gutted. Noxious Fumes is a Power that ticks poison every turn — play it once and it works forever, no matter what Doormaker does to your hand. After Image provides Block on every card play without needing to draw specific cards.

Avoid Shiv-heavy builds against Doormaker. Shivs require high card volume, and Doormaker’s draw prevention and cost increases destroy that game plan.

Defect: Orb builds are naturally resilient. Once orbs are in slots and Focus is scaled, your damage and defense happen passively. Doormaker can mess with your hand, but it can’t remove orbs from their slots. Defragment, Capacitor, and Electrodynamics are your priority plays in the opening turns.

Regent: Get your key Powers and Star generators online before phase 2. Stars persist between turns regardless of hand state. If your Star economy is running, Doormaker’s hand disruption matters less because Stars provide value independently.

Necrobinder: Doom stacking over many turns is risky because Doormaker might exhaust your Doom-applying cards before you stack enough. Play Doom cards aggressively in the early turns. Osty keeps attacking even when your hand is empty, which gives Necrobinder a damage floor that other characters don’t have.

For a deeper breakdown of this fight, including phase timings and community-tested counter-strategies, see our Doormaker deep dive guide.

Queen

Queen hits hard and defends harder. High raw damage output combined with strong defensive mechanics that punish unscaled decks. If your damage numbers aren’t high enough, her Block just absorbs everything and her counterattacks end you.

This is a straightforward fight in the sense that there are no gimmicks. Queen doesn’t warp rules or change behavior based on your plays. She simply has high stats and tests whether your deck can match them.

General strategy: Your deck needs to be finished. No half-built archetypes survive. You need your scaling engine fully online by turn 2 and enough defense to survive hits in the 40-50 damage range. Potions are not luxury items here — use your best offensive potion on the turn where it deals the most damage.

Ironclad: 15+ Strength or the Barricade + Body Slam engine. Those are the two paths that consistently win. Limit Break doubling your Strength is the highest ceiling, but you need to survive long enough to use it. Reaper with high Strength provides sustain that keeps you in the fight when the HP math gets tight.

Silent: Wraith Form buys the turns you need to set up a lethal poison stack or Shiv burst. Without Wraith Form, you need Footwork stacking to generate enough Block to survive the big hits. Catalyst is your win condition — 60+ poison into Catalyst ends the fight.

Defect: Full orb build with high Focus. Frost orbs need to generate 15+ Block per turn to survive. Lightning orbs need to deal significant passive damage. The fight is winnable with orbs alone if your Focus is at 4+.

Regent: This is your hardest matchup. Regent needs turns to build Stars, and Queen doesn’t give you breathing room. Front-load your Star generation and find opportunities to spend them on massive damage turns. Defensive Star plays keep you alive, but they delay your kill timeline.

Necrobinder: Doom is strong against Queen if you can survive long enough to stack it. Queen’s high HP means the Doom threshold is high, so you need significant stacking. Pair Doom with consistent direct damage to chip her HP into range.

Test Subject

The adaptive boss. Test Subject changes its behavior based on what you play. Attack too much and it counters with defense and punishing retaliations. Block too much and it stacks power that becomes unmanageable. It reads your patterns and exploits them.

General strategy: Alternate your approach. Don’t fall into a predictable rhythm of attack-attack-attack or block-block-block. Mix offense and defense within the same turn. Cards that provide both damage and Block simultaneously are excellent because they don’t commit you to one pattern.

Read the intent icons. Test Subject telegraphs what it’s going to do. When it shows a massive attack, block. When it shows a buff or setup turn, attack hard. When it shows a counter-stance, play the opposite of what it expects.

Ironclad: Flame Barrier provides Block and retaliatory damage in one card — exactly what this fight wants. Shrug It Off draws a card while blocking, keeping your options flexible. Avoid going all-in on Strength unless you can also generate meaningful Block. A balanced Ironclad deck handles this better than a hyper-offense build.

Silent: Accuracy + Shivs gives you small, frequent damage that doesn’t trigger the big counter-responses. Dodge and Roll provides Block that carries to the next turn. Malaise or Piercing Wail can shut down Test Subject’s big attack turns. The Silent’s natural flexibility makes this a comfortable matchup.

Defect: Frost and Lightning orbs together give you attack and defense every turn without committing to either pattern through card plays. The orbs do both simultaneously, which confuses Test Subject’s adaptation. Glacier is the single best card for this fight.

Regent: Regent’s Star system lets you hold resources and respond to whatever Test Subject presents. Don’t commit Stars until you see the intent. Reactive play is Regent’s strength, and this boss rewards it.

Necrobinder: Doom stacking is independent of the attack/block pattern. Apply Doom while making mixed plays, and eventually the threshold kills Test Subject regardless of its adaptive stance. Osty provides passive damage that doesn’t read as “attacking,” which can help avoid triggering counter-responses.

Act 3 Preparation Checklist

Before you hit the Act 3 boss, ask yourself these questions:

Is my damage scaling online? Flat damage won’t cut it against any Act 3 boss. You need Strength, poison, Focus, Stars, or Doom at meaningful levels.

Can I block 40+ damage per turn? All three bosses can hit in this range. If your defense tops out at 20 Block, you’re going to bleed out.

Do I have at least 2 Powers in my deck? Powers provide persistent value that can’t be disrupted (except by Doormaker’s exhaust, but once played they’re safe). Demon Form, Noxious Fumes, Defragment, Wraith Form — these win Act 3 fights.

Did I save a potion? A single well-timed potion can be the difference between a win and a loss. Don’t burn them on hallway fights in Act 3.