At first glance, Slay the Spire has three Acts. When you defeat the Act 3 boss and beat the game, however, you get an interesting cutscene in which you encounter a large, beating heart. You hit it for a bunch of damage, then fall unconscious before the game ends. This might seem rather strange, and for good reason. The game actually has a secret fourth Act and final boss — the Corrupt Heart — that you can only unlock after beating the base game. In this guide, we’ll cover everything you need to know about the Corrupt Heart in Slay the Spire, including how to unlock and beat the elusive Act 4.
Let’s get started!
Unlocking Corrupt Heart
If you want to get the true Slay the Spire ending where you beat Corrupt Heart, you first need to unlock Act 4 by defeating an Act 3 boss with the Ironclad, the Silent, and the Defect. The Watcher was added after release, so you don’t have to beat Act 3 with her to unlock Act 4.
Collecting the Keys
To unlock Act 4, you’ll also need to collect the Ruby Key, Emerald Key, and Sapphire Key. To collect the Ruby Key, you need to reach a rest site and then use the Recall option. To collect the Emerald Key, you need to fight a special elite encounter that’s marked on your map with a flame-like pattern (as shown in the image above). Finally, to get the Sapphire Key, you need open a non-boss chest and choose the Sapphire Key over the relic inside.
This is part of what makes Act 4 so challenging. To even unlock the next Act, you need to first face a tougher elite, give up a rest site, and give up a relic. Plan you run accordingly if you want to fight Corrupt Heart and truly beat Slay the Spire!
Spire Shield and Spire Spear
Act 4 is not just a fight with Corrupt Heart. You start with a rest site, followed by a merchant. After that, you face an elite encounter against the Spire Shield and Spire Spear. You don’t get to heal between this fight and the Heart, so be careful.
This fight uses the Surrounded mechanic, meaning that whichever enemy is behind you deals 50% extra damage. Targeting one of the enemies with a card or potion turns you to face them, making the other enemy the one now behind you (and thus the one dealing 50% extra damage). Note that Smoke Bomb potions don’t work in this encounter unless one of the two elites is defeated.
Spire Shield starts out with 110 HP and Artifact 1. Spire Shield has three different moves:
- Bash: Deals 12 damage and has a 50% chance to apply -1 Focus to Defect or -1 Strength to everyone else.
- Fortify: Gives Spire Shield and Spire Spear 30 Block each.
- Smash: Deals 34 damage and gives Spire Shield Block equal to damage dealt.
Its attack pattern is as follows:
- Turn 1: 50% chance to use Bash or Fortify.
- Turn 2: Whichever move was not used in Turn 1.
- Turn 3: Smash
Spire Spear starts out with 160 HP and artifact 1. Spire Spear has three different moves.
- Burn Strike: Deals 5×2 damage and adds 2 Burn cards to your discard pile.
- Piercer: Gives Spire Spear and Spire Shield 2 Strength.
- Skewer: Deals 10×3 damage.
Its attack pattern is as follows:
- Turn 1: Burn Strike
- Turn 2: Skewer
- Turn 3: 50% chance to use Burn Strike or Piercer.
- Turn 4: Whichever move was not used in Turn 3.
- Repeat Turns 2–4.
Now we get to the true final boss of Slay the Spire — the Corrupt Heart. This boss starts out with 750 HP, Beat of Death 1, and Invincible 300. Beat of Death 1 deals 1 damage to you each time you play a card. Invincible 300 means that Corrupt Heart can only take a maximum of 300 damage in a turn. This means you will have to fight Corrupt Heart for a minimum of three turns.
On Turn 1, Corrupt Heart uses the move Debilitate. Debilitate applies 2 Vulnerable, Weak, and Frail, respectively. Then it shuffles a Dazed, Slimed, Wound, Burn, and Void into your draw pile. Then, starting from Turn 2 onwards, Corrupt Heart uses either Blood Shots or Echo (a 50% chance for each), followed the next turn by the move it did not use. Blood Shots does 2×12 damage. Echo deals 40 damage. Starting on Turn 4, Corrupt Heart will use Buff every three turns. Buff removes all Strength debuffs and gives Corrupt Heart 2 Strength, as well as an additional buff based on the number of times the Buff move has been used.
- First buff is Artifact 2
- Second buff is Beat of Death 1
- Third buff is Painful Stabs
- Fourth buff is Strength +10
- Fifth buff and up is Strength +50
Beating Corrupt Heart
As you can see, Corrupt Heart hits hard and Beat of Death is a nasty mechanic. It’s a good idea to play defensive, but if you take too long in the fight, Corrupt Heart’s Strength gain will overwhelm you.
A good way to weather Corrupt Heart’s assault is with debuffs like Strength Reduction and Frail. Strength Reduction is especially nice here because Corrupt Heart’s Blood Shots attack deals 2×12 damage, meaning you can reduce that to zero easily. Just remember that whenever Corrupt Heart uses Buff, all strength reduction is removed.
You can also aim for abilities that trigger when you take damage. For instance, Thorns deals 3 damage to the enemy when you take damage. These abilities are really good against Corrupt Heart because of Blood Shots. Since it hits you twelve times, Thorns deals 36 damage back.
Finally, Tungsten Rod is one of the best non-hero-specific relics for this fight, as it reduces damage you take by 1. This completely counters Beat of Death 1, so it is a relic to look out for if you can.
One of my favorite ways to play the Ironclad is with a “the best defense is a good offense” approach, complete with high attack damage and plenty of Strength buffs. this won’t work against the Corrupt Heart. You can deal 300 damage in one turn at most, and between their hits and Beat of Death, they’ll kill you first every time.
Luckily for us, the Block build can be quite strong against Corrupt Heart. Body Slam does damage equal to your Block, allowing you to build up a huge defense to weather Corrupt Heart’s assault while still getting big damage.Corrupt Heart’s Strength buffs will overwhelm you even in a high Block build if you take too long, so Body Slam is essential.
The other key card is Flame Barrier. Flame Barrier gives us 12 Block and deals 4 retaliatory damage, which increases to 16 Block and 6 retaliatory damage when upgraded. The Block is very nice, of course, but this card absolutely punishes Blood Shots, dealing either 48 or 72 damage back to Corrupt Heart whenever it uses the move. It’s also worth noting that since this damage is dealt to them on their turn, it gets around that pesky only 300 damage thing you have to worry about on your turn, which may prove relevant.
The Silent can have solid success against Corrupt Heart with both the Poison build and Shiv build. The Poison build can be tricky to get going, but will pile on the damage once it does. One nice thing about this build is that it builds up cumulative stacks of poison, meaning you can deal big damage without having to play a bunch of cards every turn. This helps counteract Beat of Death.
The Shiv build is probably the Silent’s best build, and can be quite effective against Corrupt Heart. However, the Shiv build absolutely requires After Image or Tungsten Rod to have a chance. Since the Shiv build relies on playing all the cards — all of them, all the time — Beat of Death will absolutely destroy us if we don’t have either After Image or Tungsten Rod.
One of the strongest Defect builds is the zero cost build. This build functions very similarly to the Shiv build mentioned above, as it involves playing a bunch of 0-cost cards and piling on the damage. However, if you cannot get a Tungsten Rod to counter Beat of Death, this build will almost always lose.
My personal favorite Defect builds for fighting Corrupt Heart are the Frost Orb build and Lightning Orb build. The Frost build functions very much like the Ironclad’s Body Slam build. You build up a ton of Block, then dish out the damage with Blizzard to give you that nice balance of offense and defense. It’s pretty straightforward, and it can be quite effective.
The Lightning build is a very offense-focused build. This is fairly risky against Corrupt Heart, but it does have one key card that makes it very strong — Static Discharge. Whenever you take unblocked attack damage, it channels one Lightning Orb (two if upgraded). Unfortunately, it triggers on unblocked attack damage and not any old attack damage, but it is still a great counter to Blood Shots, allowing you to pile on the damage.
It is no question that the Watcher’s best build is the stance-switching Infinite build. However, this build runs into the same problem as the Shiv and 0-cost build. If you have a Tungsten Rod you can do it — otherwise, it will just kill you.
I personally like the Pressure Points build if you can get it online here. This functions similarly to the Poison build, only better. It is arguably harder to assemble, but if you can trim your deck down and get several upgraded Pressure Points, you’ll be quite effective against Corrupt Heart.
Divinity/Smite builds are also good options for fighting Corrupt Heart. If you can consistently get into the Divinity stance, you will be in a very good position to crush Corrupt Heart. After all, times three damage is times three damage. Smites can also be quite effective here, as they hit hard, not requiring you to play a bunch of cards and suffer the cruel whims of Beat of Death.
Finally, don’t get fooled by Vault. Vault is a solid Watcher card that gives you an extra turn. However, it does not reset Corrupt Heart’s invincible 300 count, so it’s not nearly as good as it normally would be.
Join the High Ground!
Now you should be ready to take on Corrupt Heart and truly slay 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.