Slay The Spire’s hidden final boss can only be unlocked by mastering the three base characters. Each carries one of the three keys you need to progress into the last act. You are rewarded with a single attempt against the game’s most challenging enemy, which can easily wipe out an unprepared deck.
The result is that you’ll want to plan carefully both for unlocking the heart and for the bossfight itself. Not every deck that can defeat the act-three bosses will be able to carry you beyond this additional finish line. Knowing how to prepare for this final boss can save you some heartache on a lost run.
Unlocking The Three Keys
The first step towards unlocking the final act is todefeat Act Three at least one time with each characteramong theIronclad, Silent, and Defect.
Each one unlocks a different key to be collected in future runs. To challenge the Heart, you’ll need tocollect all three keys in a single run.
The Watcher does not unlock a key but can collect the keys unlocked by the other characters.
Once all three keys are unlocked, there will be anemblem next to your usernamein the top left. This is used totrack which keys you have collected in a run.You will need all three when you defeat the boss of the third act.
The Ruby Key
The Ironclad’s key is the simplest to collect once unlocked. When youreach a campfire,you will have a new option, to’recall'. Meditating at the campfire gives you thered keyatthe cost of not resting or upgrading a card.
The best time to do this is during the first act, when you’ll have fewer good cards in need of upgrading and less need for healing compared to the tougher fights found later.
The Sapphire Key
The Defect’s keyreplaces the loot of non-boss chests. When you open a chest (there will always be one at the mid-point of each act), the item inside will be listed alongside the blue key.
You can only take one item, meaning theblue key will cost you the loot the chest would otherwise contain.
Taking the chest loot will mean theblue key will be offered again on the next chest.
you’re able to comfortably take this key during any of the acts when the treasure offered in the chest doesn’t add anything to your character’s build.
Items that override chest loot have an impact on the blue key.
The Matryoshka causes the chest to have two relics. Only one of them will be linked to the key, and the other can be safely looted. N’loth’s Hungry Face causes the chest to be empty, having neither the normal loot nor a chance at the key.
The Emerald Key
The Silent’s key is the hardest to collect within a run and the only one that requires you to follow a specific path when climbing the Spire.
Check your map; one of the elite encounters of each Act will have aflame decalon it. This Elite will be stronger,boasting some extra health and a fight-long buff,dependingon the act you fight it in.
The best act to get the Emerald Key in is dependent on the character and deck you’re using. The Ironclad’s early strength and healing from their starter relic mean they can challenge elites in Act One more easily than the other characters.
The Silent’s slower buildup and combo playstyles make them very effective against some of the Act Three elites.
In general,avoid Act Two elites entirelyunless your deck is especially powerful at the end of Act One.
Act Four
Act four has no normal encounters or events available. You willalways encounter the same sequenceof map nodes.
The rest site and merchant behave as normal: You’ll have no use of the rest site for healing, so you can either use it to upgrade a card oractivate a camping relic, such as the pipe or shovel.
The Shield And Spear
This elite duo is your final fight before the heart, and youwon’t have an opportunity to heal afterfighting them, so you should aim to conserve your HP and consumables.
You’ll have theSurrounded Debuffwhile both enemies are alive, a unique mechanic to this fight. Theenemy you turned your back on(by attacking the other) willdeal 50 percent bonus damage.
This encourages you tosplit damageto ensure you’re always facing the current attacker, but you can also work toquickly kill one(the spear has more HP but generates less block, so it will die faster) and remove the buff from yourself.
If you have a smoke bomb potion, you will not be able to use it while Surrounded but can use it to flee the fight after defeating either enemy.
The Heart
The Heart is a worthy contender as final bosses go and has multiple mechanics that will outright disable certain decks from being able to defeat it.
If you are running any of the following decks, you should consider not collecting the third key so you win at the end of act three.
Ways To Overcome This Weakness
Infinite Loops/ Shivs/ Anger Decks
The Heart places one of every status card in your deck on the first turn of combat.This means that a loop deck with only attacks and draws will not have its normal consistency and can fail to achieve an infinite loop.
The Heart’s Beat Of Death passivedeals one damage every time you play a card. A Flash Of Steel deck cannot run an infinite loop because it will take a near-equal amount of damage.
TheMedical Kit shop reliccan exhaust unplayable status cards.
TheOrnamental Fan relic, Afterimage power and Rage skillcan produce enough blocks to offset Beat of Death.
One Turn Kill Combos
The Heart’s Invincible Bufflimits the damage it can take in a turn to 300 of its 750HP(changed by ascension level).
If you’re able to pull off your kill combo three turns in a row, the heart will not have enough time to kill most characters.
Ramp Decks (Demon Form, Omega, Barricade)
The Heart applies buffs to itself at three-turn intervals. After doing this three times, the next time will give a muchstronger buff that enables it to instantly kill any character.
The Intangible Buff can allow you tosurvive the instant kill attacks, giving you more time to pull off a slow combo.
After its first turn, inflicting debuffs and statuses on you, it will rotate through three moves.
An ideal deck for defeating the heart can set up its win condition quickly,dealing 750 damage before the 10th round of combat. This is the point where the Heart’s self-buffs become much stronger, and it generates more status cards to clutter your deck.
You will also need a way ofgenerating about 40 block per turn, depending on the attack pattern and buff level of the Heart.
Effects that can carry block between turns, like Calipers and Blurs, can make use of the turns the heart does not attack on.
Damage Reflection
Flame Barrier, Bronze Scales, Caltrops
The Heart’s 12-hit multi-attack will cause it to take a lot ofdamage from damage reflection effects.
Damage Reduction
Disarm, Torii, Tungsten Rod
The Heart’s 12-hit multi-attack means thatper-hit damage reduction is highly effective.
Strong Singular Cards
Fiend Fire, Reinforced Body, Meteor Strike
Beat of Death effectpunishes chaining too many cards together.X-cost cards and other cards that efficiently spend all your energy can work around this.
Short-Term Combos
Biased Cognition, Wraith Form, Corruption
This final boss is quick and brutal: By the timethe drawbacks of these cards appear, you’ll have won or lost already.
Deck and Hand Manipulation
Scry, Exhaust, Discard
These mechanics work around the status cards the heart puts into your deck by keeping them from your hand. They also let youdelete or avoid cards that are too slow or ineffectiveto help in the boss fight.
With the right combination of racing to 750 damage and keeping up 40 block every turn, the heart will die handily. Each character has a unique victory screen for defeating the Heart, including the Watcher.
