Honkai: Star Rail — How To Defeat Borehole Planet’s Old Crater

You’re gonna need some bigger boots to squash this bug.

There are lots of enemies to beat in Honkai: Star Rail. One of the toughest among them is the Echo of War called Borehole Planet's Old Crater, also known as the Starcrusher Swarm King and the Propagation Clone. This enemy is a giant bug that is tricky to beat due to its ability to produce Stings — trap characters in Entanglement — and to throw an Ovum of Collapsed Star at your party.

You can encounter them by doing the Crown of Mundane and Divine quest on the Herta Space Station. By defeating this tricky enemy, you can gain Past Evils of the Borehole Planet Disaster, a valuable Trace Material used for characters like Black Swan, Sparkle, and Dr. Ratio.

How To Unlock Borehole Planet's Old Crater

You can unlock this Echo of War Zone by doing the Crown of Mundane and Divine Trailblaze quest.

In order to unlock this quest, you must first reach Trailblaze level 24and beat the Trailblaze mission on Belabog (Jarilo-IV).

Where To Challenge Borehole Planet's Old Crater

Borehole Planet's Old Crater Echo of War is located on the Seclusion Zone map of the Herta Space Station.

Starcrusher Swarm King Mechanics And Moves

The fight against the Propagation Clone will take you through two phases. It will have certain skills depending on which stage you are on.

Weaknesses: Physical, Ice, and Imaginary.
Resistances: Quantum and Entanglement.

Phase One

These are the Swam King's moves during the first phase:

Name	Description	How To Deal With It
Swarm King Canon	A single-target Quantum attack.	This is a normal monster attack, so deal with it how you normally would with your team.
Pyrolysis Death Beam	Deals Quantum damage to a target and the allies next to them.	Heal your characters if their HP is getting too low.
Carapace of Begotten Spawn	Enters a shield-like state where all damage is reduced. Every time it is attacked, it will summon a Gnaw Sting (an additional enemy) to a maximum of four. Causing Weakness Break while in this state will deal damage to the Gnaw Stings present and reduce their Toughness.	This is the big one. The easiest and best way to defeat this boss is by inflicting Weakness Break on it while it is in this state. However, while you're trying to do this, you run the risk of summoning more Gnaw Stings, which will cause your team to suffer more damage overall. So before the Starcrusher Swarm King can enter into Carapace of Begotten Spawn, make sure that you have inflicted as much damage as possible onto its Toughness. This will require fewer turns for you to take it out, which means you will summon fewer Gnaw Stings. When you do break its Toughness, that is the time for your team to act. It's good to save up your team's Skill Points and Ultimates for this moment. Use all your Ultimates and Skills on it now to deal as much damage as possible.

Name

Description

How To Deal With It

Swarm King Canon

A single-target Quantum attack.

This is a normal monster attack, so deal with it how you normally would with your team.

Pyrolysis Death Beam

Deals Quantum damage to a target and the allies next to them.

Heal your characters if their HP is getting too low.

Carapace of Begotten Spawn

Enters a shield-like state where all damage is reduced. Every time it is attacked, it will summon a Gnaw Sting (an additional enemy) to a maximum of four. Causing Weakness Break while in this state will deal damage to the Gnaw Stings present and reduce their Toughness.

This is the big one. The easiest and best way to defeat this boss is by inflicting Weakness Break on it while it is in this state. However, while you're trying to do this, you run the risk of summoning more Gnaw Stings, which will cause your team to suffer more damage overall.

So before the Starcrusher Swarm King can enter into Carapace of Begotten Spawn, make sure that you have inflicted as much damage as possible onto its Toughness. This will require fewer turns for you to take it out, which means you will summon fewer Gnaw Stings.

When you do break its Toughness, that is the time for your team to act. It's good to save up your team's Skill Points and Ultimates for this moment. Use all your Ultimates and Skills on it now to deal as much damage as possible.

If you have characters on your team during this phase who don't damage Toughness very well but whose attacks hit multiple enemies at once, have them target the Gnaw Stings.

Phase Two

This phase is particularly dangerous. If your team is in a tight spot after Phase One, you probably won't live long here. This phase is designed to keep the punches rolling and to kick you while you're down. The trickiness of this phase means that you really need to be familiar with the mechanics so you can exploit them and work around them.

Here are the moves the Swarm King will throw at you in Phase Two:

Name	Description	How To Deal With It
Ovum of Collapsed Star	Deals massive Quantum damage to all targets.	Ovum of Collapsed Star is annoying because of how powerful it is. After getting hit by this one or two times, you'll probably find that your team needs to be healed, so make sure your healer's Ultimate is ready or that the healer has enough Skill Points to help keep everyone alive.
Swarm King Canon	Deals Quantum damage to a single target. It deals less damage than Ovum of Collapsed Star.	This move is less powerful than Ovum of Collapsed Star, but it is still a pain to deal with. Make sure your team has enough healthso they can take one or two of these, or you might find them being defeated.
Radiating Venom	Deals Quantum damage to a single target and has the chance of Entangling them. This move also summons a Gnaw Sting.	You absolutely need a character who can clear Entaglement on your team, and you need them to do it quickly. If you don't act soon, the Gnaw Sting that this move summons will target that character. This has a great chance of taking your character out, so be careful.
Carapace of Neutered Disaster	Similar to Carapace of Begotten Spawn. This move creates a shield-like barrier, which reduces the damage Swarm King will take. When it is attacked, a Gnaw Sting or a Lesser Sting will be summoned. When Carapace of Neutered Disaster ends, it will use Ovum of Collapsed Star. By causing Weakness Break on Swarm King, it will deal damage to the surrounding Gnaw Stings and Lesser Stings and reduce their Toughness.	In order to best deal with this move, you need to cause Weakness Break quickly before it can hit you with an Ovum of Collapsed Star. If it has too much Toughness for you to whittle down in a couple of turns, attack the Gnaw Stings and Lesser Stings instead and use your healer to make sure everyone on the team has enough HP to take the upcoming Ovum of Collapsed Star.

What To Do To Prepare For Carapace of Begotten Spawn and Carapace of Neutered Disaster

Carapace of Begotten Spawn and Carapace of Neutered Disaster are two of the most deadly moves the Swarm King can do. There are some things that you can do to prepare for it before it kills off your team:

Inflict damage on Swarm King's Toughness: By dealing damage to its Toughness before it enters this state, you'll have a head start for when you need to cause Weakness Break when it enters this state. By being able to cause Weakness Break early, you will also need to attack it less, meaning that it will be able to summon fewer Stings.
Save your Ultimates and Skill Points for the Weakness Break: When you do cause Weakness Break, you need to deal as much damage to the Swarm King before it can recover. Remember to make use of its weaknesses: Physical, Ice, and Imaginary.
Heal your team just in case: If you can't cause Weakness Break in time, you'll need to make sure that your team can take the damage dealt by the Stings and by Ovum Star Collapse.
Deal some damage to the Stings using AoE Attacks: You will often be faced with multiple Stings at once, so bringing someone who can do AoE damage is important for taking them all down.

Gnaw Sting

The Gnaw Stings are particularly annoying enemies that are summoned while the Swarm King has Carapace of Begotten Spawn or Carapace of Neutered Disaster active.

Weaknesses: Physical and Ice
Resistance: Quantum

Here's what it can do:

Name	Description	How To Deal With It
Horn Clash	Deals Quantum damage to a target and inflicts one stack of Entanglement. It will prioritize targets that are already entangled.	This move is probably the most annoying one to put up with because it will completely stop one of your characters from being able to act, which can be particularly devastating if you're in a pinch. Because of this, you should bring along a character who can clear Entanglement from your other party members.
Decay Eulogy	When killed, it explodes and deals damage to the allies next to it, increasing the damage they will receive.	When there are lots of Gnaw Stings on the field, you should prioritize getting rid of them. Not only will this stop them from Entangling your team, but when you do defeat them, they will weaken their allies, including the Swarm King.

Name

Description

How To Deal With It

Horn Clash

Deals Quantum damage to a target and inflicts one stack of Entanglement. It will prioritize targets that are already entangled.

This move is probably the most annoying one to put up with because it will completely stop one of your characters from being able to act, which can be particularly devastating if you're in a pinch.

Because of this, you should bring along a character who can clear Entanglement from your other party members.

Decay Eulogy

When killed, it explodes and deals damage to the allies next to it, increasing the damage they will receive.

When there are lots of Gnaw Stings on the field, you should prioritize getting rid of them. Not only will this stop them from Entangling your team, but when you do defeat them, they will weaken their allies, including the Swarm King.

If you defeat a Gnaw Sting while the Swarm King has Carapace of Begotten Spawn or Carapace of Neutered Disaster active, its explosion will hit the Swarm King and cause it to summon another Gnaw Sting.

How To Deal With Lesser Stings

Lesser Stings are summoned by the Swarm King when it has Carapace of Neutered Disaster active during Phase Two.

Weaknesses: Physical, Fire, and Imaginary.
Resistances: Ice.

These are the Lesser Sting's moves:

Name	Effect	How To Deal With It
Bursting Detonation	It explodes, dealing Wind damage to its targets. It has a high chance of inflicting Outrage.	Make sure your team has enough HP to deal with its damage.
Prepare to Fight	Enters a charge state. It will use Bursting Detonation during its next action.	If you can, kill it before it can explode.
Entomon Eulogy	When defeated, it deals Wind damage to its allies and has a high chance of increasing the damage its allies will receive.	Take advantage of its allies' weakened states moving forward.

What Kinds Of Characters Should You Bring?

The two kinds of characters you need most are those who can Dispell Entanglement and those who can inflict Weakness Break.

By Dispelling Entanglement, you will be able to prevent your characters from falling from repeated attempts to Entangle them and increase their ability to survive the battle.

Causing Weakness Break on the Swarm King is also extremely important and the easiest way for you to defeat it, so it's super important to bring characters along who can take down its Toughness.

Character	Type	Role
Dr. Ratio	Imaginary Hunt	Weakness Break Follow-Up Attacks Imaginary damage Main DPS Can inflict Imprisonment on Weakness Break
Yukong	Imaginary Harmony	Support (increases Attack, Crit Rate, and Crit Damage) Imaginary damage
Lynx	Quantum Abundance	Healer Can dispel Entanglement
Herta	Ice Erudition	AoE attacker Can cause Freeze on Weakness Break Ice damage
Misha	Ice Destruction	AoE attacker Can cause Freeze on Weakness Break Ice damage
Ruan Mei	Ice Harmony	Support Break Effect Ice damage

Luocha	Imaginary Abundance	Support Healing Imaginary
Shushang	Physical Hunt	Main DPS Weakness Break Gains buffs when an enemy has Weakness Break Physical damage
Sparkle	Quantum Harmony	Support (increases Skill Points)
Luka	Physical Nihility	Damage Over Time DPS Physical damage
Clara	Physical Destruction	Can dispel Debuffs (including Entanglement) on her Can counter the damage she takes Physical damage
Huohuo	Wind Abundance	Healer Can dispel Entanglement
Bailu	Electric Abundance	Healer Can prevent allies from being knocked down

Rewards for Beating Borehole Planet's Old Crater

By beating Borehole Planet's Old Crater, you will gain the following rewards:

Past Evils of the Borehole Planet Disaster (Trace level-up materials)
Musketeer of Wild Wheat (Relics)
Thief of Shooting Meteor (Relics)
Lucent Afterglow
Light Cones
Credits

Characters Who Use Its Trace Materials

This Echo of War zone drops a Trace Material called Past Evils of the Borehole Planet Disaster, which can be used to level up certain characters' Traces.

These are the characters who use Past Evils of the Borehole Planet Disaster:

Black Swan
Sparkle
Ruan Mei
Dr. Ratio
Xueyi
Misha