In Slay the Spire, no run looks exactly the same as the next. In addition to the various characters you can choose from and relics you can earn, the game throws a wide variety of challenging enemies your way. Among these enemies are the game’s bosses, of which there are nine in total — three for each of the game’s three acts. By pitting you against one randomly determined boss per act, Slay the Spire keeps you on your toes and always on the watch for the best possible strategy. In this guide, we’ll go over each of the Slay the Spire bosses to help you prepare for your next run.
Note that this guide won’t cover the Heart, as it’s an entity deserving of its very own guide. We also won’t cover ascension levels and how those can effect boss fights, as we’ll also revisit those mechanics in a later guide.
With all that in mind, let’s get started!
Act 1 Bosses
Let’s start with the Act 1 bosses in Slay the Spire — Slime Boss, Hexaghost, and The Guardian. We’ve ordered them by difficulty below so you’ll know exactly what to expect when you start your next run.
Slime Boss is the first boss we’ll cover. It’s definitely the easiest of the bosses in the Slay the Spire, as it has a pretty simple rotation and starts combat with only 140 HP.
Like we said, Slime Boss has a very simple rotation. On its first turn, Slime Boss will use Goop Spray to add three Slimed cards to your discard pile. This is a 1-cost status effect with Exhaust, so it will disappear once played. Next, Slime Boss will use its turn to Prepare (denoted by three question marks above its head). Finally, it will Slam and deal 35 damage in a single hit. From there, just rinse and repeat.
Slime Boss also has an interesting mechanic called Splitting. If you deal at least 70 damage to Slime Boss, it will split into two new enemies instead of taking its turn. The resulting Acid Slime and Spiked Slime will both start with HP equal to Slime Boss’s HP when it splits.
Acid Slime is not quite as predictable as the Slime Boss. It has a 30% chance of using Corrosive Spit each turn (dealing 11 damage and putting two Slimed cards into your discard pile), a 30% chance of using Tackle (which does a flat 16 damage), and a 30% chance of using Lick (which applies two Weak). If you deal damage equal to 50% or more of the Acid Slime’s HP, it will skip its action to split into two Acid Slimes, each with HP equal to what the original Acid Slime had when it split.
Spiked Slime has a 30% chance of using Flaming Tackle (which does 16 damage and puts two Slimed cards into your discard pile), and a 70% chance of using Lick (which applies two Frail). Just like the Acid Slime, the Spiked Slime splits at 50% or less health.
The strategy for beating Slime Boss is fairly straightforward. You’ll want to take advantage of the splitting mechanic to deny Slime Boss its Slam move, so try to hit that 70+ damage marker before Turn 3. It’ll make the fight much easier.
From there, you’ll want to split (or kill) the smaller slimes each time they’re about to get a big hit in. The rotation isn’t as predictable, but you can use the game’s Intent mechanic to see which slimes to prioritize.
This fight clearly favors aggressive builds, but if you’re tactical with your Block and debuffs, you can weather the bigger attacks and still take the Slime Boss down.
Hexaghost is our next boss. It doesn’t pose much of a challenge as long as you don’t take too long fighting it (more on that in a second). Hexaghost starts with 250 HP.
On its first turn, Hexaghost will use Activate. This move does nothing, meaning you get a free turn. But if you’re feeling really good about this, remember that on its next turn, Hexaghost will use Divider. This deals an amount of damage equal to your current HP divided by 12, then plus 1. It deals this damage six times. If you have 43 HP like in the screenshot above, for example, the damage calculation will look something like this:
((43 / 12) + 1) * 6 = 24
After this hefty attack, Hexaghost follows a specific attack rotation signified by a number of green flames. At zero flames, it uses Sear to deal 6 damage and shuffle a Burn into your deck. Burn is an unplayable status card that deals 2 damage to you at the end of the turn. At one flame, it uses Tackle (dealing 2×5 damage). At two flames, it uses Sear again. At three flames, it uses Inflame (gains 2 Strength and 12 Block). At four flames, it uses Tackle again, and at five flames, it’s back to Sear. Then, at six flames, it uses Inferno (deals 2×6 damage and shuffles three Burns into your deck, then upgrades all Burns so they now deal 4 damage at the end of turn).
After Inferno, the whole cycle starts all over again.
We said before that you don’t want to take a long time with this fight. The slower you go, the more Burns you’ll have clogging up your deck and slowly killing you. The best way to handle this is to use Hexaghost’s lower-damage turns (Sear and Tackle) to get your big hits in, then just play defensively on the Divider. If you have a slower build, you just need to hope you get lucky with the Burns.
The Ironclad has a specific counterplay option to Hexaghost that makes this fight a lot easier. If you look on the map and see that Hexaghost will be your Act 1 boss, you can add a Fire Breathing to your deck. Fire Breathing is a 2-cost power that makes it so that whenever you draw a status card, you deal 6 damage to all enemies (10 if upgraded). This turns Hexaghost’s own burns against it.
The Guardian is the final Act 1 boss. It begins combat with 240 HP.
The Guardian starts combat in Offensive mode. While in Offensive mode, The Guardian will always use the same attack pattern. It starts with Charging Up to gain 9 Block), then Fierce Bash to deal 32 damage). It follows this with Vent Steam, which applies 2 Vulnerable and 2 Weak, and finally Whirlwind, which deals 5×4 damage.
Below The Guardian’s health bar, there’s a circular icon with the number 30 next to it. This is the Mode Shift counter. Whenever The Guardian takes damage, the counter goes down by that number. When the counter hits zero, The Guardian changes to Defensive mode, and gains 20 Block.
The Defensive mode pattern starts with the aptly named move Defensive Mode, which gives The Guardian Sharp Hide. This ability deals 3 retaliatory damage whenever you play an attack card. Unlike the Thorns ability, Sharp Hide does not care about number of hits. Next, The Guardian uses Roll Attack to deal 9 damage, and finally Twin Slam, which deals 8×2 damage, removes Sharp Hide, and switches The Guardian back to Offensive mode.
The cycle repeats once The Guardian switches back to Offensive mode. However, whenever The Guardian switches back to Offensive mode, their Mode Shift counter goes up by 10 (meaning you’ll need to deal 40 damage to switch it back to Defensive mode, then 50, and so on).
You’ll ideally want to trigger Defensive mode before The Guardian can hit you with Fierce Bash. This means dealing at least 39 damage in the first two turns. An important thing to note is that The Guardian gains 20 Block as soon as Defensive mode is activated, so you’ll want to get as close to zero on the Mode Shift counter as you can, then trigger Defensive Mode with one big hit to maximize the damage you deal before the Block kicks in.
Once The Guardian is in Defensive mode, be careful with your attacks, since you’ll take 3 damage for each attack card played. Think of it as a mode shift as your own — play defensively while it’s in Defensive mode, and offensively while it’s in Offensive mode. If you time it right, you can avoid any big hits and win.
Act 2 Bosses
Now we move on to the Act 2 Slay the Spire bosses. The three bosses for this act are Bronze Automaton, The Champ, and The Collector. Now we get minions added into the mix, making these boss fights even more interesting.
Bronze Automaton is our first Act 2 boss. It starts with 300 HP and 3 Artifact.
On its first turn, Bronze Automaton will use Spawn Orbs to creation two minions called Bronze Orb. From there, it follows a pattern of using Boost to gain 3 Strength and 9 Block, Flail to deal 7×2 damage, Hyper Beam to deal 45 damage, and Stunned (which does nothing).
Bronze Orbs will have 52–58 HP when summoned. They have a 75% chance of using Stasis (steals the rarest card in your draw or discard pile, a 7.5% chance of using Beam (deals 8 damage), and a 17.5% chance of using Support Beam (gives Bronze Automaton 12 Block). They will never use the same move three times in a row.
If you kill a Bronze Orb, your stolen card is returned directly to your hand. Any cards you have in Stasis will not trigger effects be affected by other cards (you can’t reduce a card’s cost while it’s in Stasis, for example).
The Bronze Orbs are clearly a problem here, as they can steal good cards and be pretty nasty besides. The real trick is to balance focusing the Bronze Orbs and the Automaton itself. It’s great to kill the Orbs quickly, but if you spend too many resources on them, you won’t be damaging the Automaton and will just lose.
If you’re playing a very high damage build, you can probably just focus down the Bronze Automaton and ignore the Orbs, but that requires a lot of damage.
The Champ is the next Act 2 boss, and enters combat with a whopping 420 hp. I guess The Champ likes to blaze it.
The Champ has two phases. During Phase 1, it will use Taunt to apply 2 Weak and 2 Vulnerable every four turns. Outside of that, it has a 15% chance of using Defensive Stance to gain 15 Block and 5 Metallicize (which grants 5 Block at the end of its turn), a 15% chance to Gloat (gains 2 Strength), a 25% chance to Face Slap (deals 12 damage and applies 2 Weak and 2 Vulnerable, and a 45% chance to Heavy Slash (deal 16 damage).
When The Champ’s HP drops below 50%, it will use Anger (removes all debuffs and gains 6 Strength), and immediately enter Phase 2. On the first turn of Phase 2, The Champ will use Execute to deal 10×2 damage. For the next two turns, it’ll repeat the Phase 1 pattern, then use Execute again. This pattern repeats until it’s defeated.
The Champ can be quite tough, but compared to many of the other bosses in Slay the Spire, it doesn’t hit quite as hard with any given move. 10×2 damage is a lot weaker than a flat 45!
What you really want to watch out for are the Strength increases and the debuffs it inflicts. Its attacks start out average, but get stronger and stronger as the fight progresses. You can use the Phase 2 shift and the Taunt turns to try and get in some big damage.
The Collector is the final Act 2 boss. It starts with 282 hp.
The Collector always starts with the move Spawn, which summons up to two Torch Heads. On turn four, it will always use Mega Debuff, which applies 3 Weak, 3 Vulnerable, and 3 Frail.
The Collector has an interesting pattern. If one or more Torch Heads are dead, it has a 25% chance of using Spawn, a 45% chance of using Fireball (deals 18 damage), and a 30% chance of using Buff (grants 3 Strength and 15 Block to itself and any living Torch Heads.
If both Torch Heads are alive, it instead has a 70% chance to use Fireball and a 30% chance to use Buff. Buff cannot be used twice in a row, and Fireball cannot be used three times in a row.
Torch Heads have 38–40 HP and always use Tackle (deals 7 damage).
As with the Bronze Automaton, you want to balance targeting the main boss and its minions. The Torch Heads aren’t super dangerous, but 14 damage per turn isn’t good to ignore. Killing them also gives you a chance to avoid damage from The Collector, as it might use Spawn. The Collector also cannot do anything about debuffs, so you can use those to great advantage in this fight.
Act 3 Bosses
Now we get to the final bosses in Slay the Spire, at least before you unlock The Heart. The three bosses for this act are the Awakened One, Time Eater, and Donu & Deca. These bosses introduce some counter play, which can be nasty. Awakened One, for example, is strong against builds that rely heavily on power cards, and Time Eater seriously nerfs any build based on playing as many cards as possible in one turn. So be ready for some tough fights.
Awakened One is the first of our Act 3 bosses. Like The Champ, it has two phases, but they’re a bit extra. It stars both phases at 300 HP, and enters combat with two Cultists by its side. It also starts with 10 Regen (heals 10 HP per turn) and Curiosity (gains 1 Strength every time you play a power card).
In Phase 1, Awakened One has a 25% chance to Soul Strike (deals 6×4 damage), and a 75% chance to Slash (deals 20 damage). Slash cannot be used three times in a row, and Soul Strike cannot be used twice in a row.
Once Awakened One reaches 0 HP, it changes its intent to Rebirth and it loses Curiosity. Rebirth starts Phase 2, healing it to 300 HP and carrying over all Strength gained from Curiosity before switching phases. On the first turn of this phase, it uses Dark Echo to deal 40 damage). From then on, it has a 50% chance to use Tackle to deal 10×3 damage, and a 50% chance to use Sludge to deal 18 damage and shuffle a Void into your draw pile (reduces your energy by one on the turn it is drawn). It cannot use either move three times in a row.
The Cultists start with 48–54 HP. They always use Incantation on turn one, which gives them 3 Ritual (grants 3 Strength each turn). Their only other move is Dark Strike, which deals 6 damage.
By the time you face the Act 3 bosses in Slay the Spire, your build is likely strong enough to just ignore minions. Focus on the Awakened One here, as you’ll probably kill the Cultists with collateral damage anyway. You also don’t want to give the Awakened One too many chances to heal with its Regen.
Also keep in mind that once the Awakened One switches to Rebirth, you won’t be able to interact with it until Phase 2 begins.
Time Eater is the next Act 3 boss. It can be a bit annoying, but it’s not too tough if you’re prepared to deal with it. It begins combat with 456 HP.
Time Eater’s most notable mechanic is its Time Warp ability. Every twelve cards you play, your turn ends automatically and Time Eater gains 2 Strength. Keep in mind that this is every twelve cards — the counter carries across turns.
If you get Time Eater to below 50% HP, it will use Haste on its next turn to remove all debuffs and heal back to 50% HP.
Outside of that, Time Eater has a 20% chance to use Ripple (gains 20 Block and inflicts 1 Vulnerable and 1 Weak), a 45% chance of using Reverberate (deals 7×3 damage), and a 35% chance of using Head Slam (deals 26 damage and applies 2 Draw Reduction). Draw Reduction means you’ll draw one less card for a number of turns equal to your DR stack.
Obviously, Time Eater is a real pain for decks that like to plays tons of cards in a turn (such as a Silent Shiv deck). While challenging, those decks can still beat it.
What you want to do is try and end your turn on the twelfth card, so that you don’t miss out on part of a turn. You just need to get into the habit of playing enough cards so the math works out in your favor. It can be a tricky ability to navigate at first, but you’ll overcome the main hurdle of this boss once you do.
Donu & Deca
Donu & Deca is the final boss of Act 3. Donu is donut-shaped, and Deca is a decahedron. They each have 250 HP and 2 Artifact at the start of combat.
Donu always starts off with Circle of Power (grants 3 Strength to both Donu and Deca). Then it alternates between Beam (deals 10×2 damage) and Circle of Power. Deca always starts with Beam (deals 10×2 damage and adds two Dazed cards into your discard pile), then alternates between Square of Protection (grants 16 Block to both Donu and Deca) and Beam.
This is the most straightforward of the bosses in Slay the Spire, but also usually the toughest. The real key to winning this fight is to try and focus on killing Donu first. Donu’s Strength buff gets out of hand fast, so do everything you can to kill Donu first, then focus on Deca.
Join the High Ground
And there you have our guide to all the Slay the Spire bosses — thanks for reading! Now that you know how they act and how to counter them, you can slay them and the Spire. Let us know your thoughts in the comments below, and don’t forget to subscribe to our weekly newsletter for more gaming content.