The Plasmium Phial is one of the best tools in Hollow Knight: Silksong, featuring 20 charges that can boost your health beyond the maximum by injecting yourself up to three additional times before big fights. To obtain this powerful healing tool, you'll need to complete the "Alchemist's Assistant" quest in the Wormways area by collecting three Plasmium samples using the Needle Phial.
| Feature | Details |
|---|---|
| Tool Type | Red Tool (Healing) |
| Location | Wormways (Alchemist Zylotol) |
| Requirement | Simple Key + Alchemist's Assistant Quest |
| Max Charges | 20 total (3-6 active) |
| Refill Cost | 50 Rosaries (initially) |
| Upgrade Available | Plasmium Gland (Advanced Alchemy quest) |
| Special Mechanic | Overdose state at 9 masks |
This comprehensive guide covers everything you need to know about obtaining, using, and mastering the Plasmium Phial in Silksong – from basic acquisition to advanced overdose strategies that can make Hornet nearly invincible. Whether you're struggling with tough bosses or exploring dangerous platforming sections, this tool will become essential to your survival in Pharloom.
Contents
The Plasmium Phial is a Tool in Hollow Knight: Silksong that allows Hornet to inject herself with a phial filled with Plasmium, giving her one Plasmium mask per use. Unlike the standard Bind healing mechanic that requires silk, this tool provides an alternative healing method that can be used anytime – even when your silk meter is empty.
The tool's most unique feature is its ability to grant temporary health masks beyond your natural maximum. These blue Plasmium masks appear above your regular health bar and persist until you rest at a bench, die, or enter a cutscene. This makes the Plasmium Phial incredibly valuable for tackling difficult boss encounters or navigating treacherous platforming sections where extra health can mean the difference between success and failure.
While Bind healing restores three masks at once (when you have sufficient silk), the Plasmium Phial only heals one mask per use. However, its advantages include:
Before you can access the Wormways and begin the Plasmium Phial quest, you'll need a Simple Key. The easiest Simple Key is found right at the start, sold by the vendor in Bone Bottom for 500 Rosary Beads. Alternative locations include finding them throughout various areas of Pharloom, but purchasing one early ensures quick access to this valuable tool.
The Wormways are an optional area accessed through the Moss Grotto — the area is to the west (left) of the Moss Grotto. It can be accessed with a Simple Key. To reach the locked door:
Once inside the Wormways, your first objective is locating the quest giver. You'll find a workshop in the Wormways with an NPC called Alchemist Zylotol. Talk to him to begin the "Alchemist's Assistant" quest. Navigate through the winding tunnels heading upward and to the left until you reach his laboratory at the top of the area.
Critical Step: After accepting the quest, sit down on the bench to his left and equip the Needle Phial to your trap slot. Failure to equip the Needle Phial before leaving will mean you cannot collect samples when you reach the plasmium. This is essential – without the Needle Phial equipped, you cannot extract Plasmium from the glowing buds.
Two of the plasmium are located at the southernmost portion of the Wormways, while the third is on your way there. Each plasmium takes the appearance of a bright blue liquid-filled flower, meaning you cannot miss it once you see it.
The first Plasmium is located in the maze of tunnels below Alchemist Zylotol's room in the Wormways.
In the maze of chambers at the southwest corner of the Wormways.
Found near the south entrance from Moss Grotto in the Wormways, above the Bonegrave room.
To extract Plasmium, find the blue glowing bulbs and use the Needle Phial tool. Fully charge it to stab into Plasmium, extracting it. The process requires:
Bring the extracted essence to Alchemist Zylotol to complete the quest and earn the Plasmium Phial. Return to his laboratory and speak with him to receive your reward. The tool will be automatically added to your inventory.
When refilling the phials at a bench, it will draw from a reserve of Plasmium. Hornet can only carry up to 20 Plasmium in her reserve, regardless of how many Tool Pouches she has collected. The system works as follows:
Initially the plasmium can only be restored by talking to Alchemist Zylotol. To upgrade the Plasmium Phial, you'll need to progress deeper. The reserve can be refilled by speaking with Alchemist Zylotol in the Wormways and paying him 50 Rosaries.
This creates an early-game limitation where you must return to the Wormways for refills, making strategic use important until you obtain the upgrade.
Talk to Alchemist Zylotol again to unlock the 'Advanced Alchemy' quest. For this quest, search the Wormways — it has changed after progressing the story — and use the Needle Phial on enemies that have evolved with Plasmium.
The Advanced Alchemy quest requires gathering 10 Plasmified Blood samples from infected enemies:
There's a breakable wall near Plasmium location #3. It leads to a chamber where you can battle a boss named Plasmified Zango, who used to be Zylotol's assistant. Extracting Plasmified Blood from him using the Needle Phial will reduce his maximum HP by 250.
Boss Strategy:
Give x10 Plasmified Blood to Zylotol to get the Plasmium Gland. This key item allows Hornet to generate Plasmium Phial charges without restoring the reserve at Zylotol — you can restore charges at any bench like a normal tool from now on.
This upgrade fundamentally changes how the tool functions:
If you restore 9 masks with Plasmium — these are called Lifeblood Masks and they're distinguished by a blue icon — all your regular masks will be replaced with blue masks. In this state, she will passively recover one Mask every 6 seconds (similar to the Joni's Blessing + Hiveblood synergy from Hollow Knight).
There are multiple methods to reach 9 Plasmium masks:
Benefits:
Drawbacks:
Plasmium Phial's special Overdose effect can be triggered easily and reliably by craft binding. The Architect Crest offers:
For exploration-focused players, combine Plasmium Phial with:
To cover for its weakness of not being able to heal unless you go in and do a Silk Bind burst, it's recommended to have Plasmium Phial equipped and use it to have more masks to allow you to jump in and use Silk Bind to restore HP without much risk of dying.
If Hornet has the Pollip Pouch equipped, the Plasmium Phial will instead give Hornet a poisoned mask when used. This mask will quickly disappear on its own after 3 seconds. However, when it is removed, it will create a large cloud of poison around Hornet.
This creates an offensive variant:
When using Multibinder in overdose state:
The Plasmium Phial becomes even more valuable in Steel Soul mode:
Alchemist Zylotol claims to have been the first to discover and name Plasmium. However, it is actually the same substance as Lifeblood from Hollow Knight. Veterans of the first game will recognize:
You can technically make a "No Bench Build" with the Druid's Eye(s) being able to regenerate health, and therefore silk, infinitely. Combine with:
No, you cant get this without using a simple key to unlock the wormway door, making the Simple Key an essential requirement.
Tool Pouches increase active charges from 3 to 6, but the 20-charge reserve limit remains unchanged regardless of pouches collected.
Yes, but the Architect Crest makes it most practical due to its Craft Bind ability allowing tool regeneration without benches.
Dying, resting at a bench, going through a cutscene, or using any form of fast travel will clear this state. It's temporary by design.
No, it's optional but provides easier Plasmified Blood collection and counts toward your quest total.
You must return to Alchemist Zylotol and pay 50 Rosaries for a full refill, unless you have the Plasmium Gland upgrade.
Hollow Knight: Silksong doesn't feature multiplayer gameplay - this is a single-player tool.
For more strategies, discussions, and updates about the Plasmium Phial and other Hollow Knight: Silksong content, join these official communities:
There seem to be a bug that can happen when you get the infinite refill gland in act 3 while the phials are empty with no reserve. They will not refill ever and are basically unusable until a patch comes out.
Prevention: Always maintain some reserve charges before completing Advanced Alchemy quest.
If interrupted during the overdose transformation, you lose all Plasmium masks. Wait for safe moments before attempting the overdose transition.
Early game Rosary management is crucial. Prioritize Plasmium refills over cosmetic purchases until obtaining the Plasmium Gland.
The Plasmium Phial reveals deeper connections between Hollow Knight games. Alchemist Zylotol's research into what he calls "Plasmium" is actually studying Lifeblood, suggesting ancient connections between Hallownest and Pharloom. His assistant Zango's transformation into Plasmified Zango serves as a cautionary tale about the substance's power.
The Hunter's Journal provides additional context: "In my home caves, when once this substance was allowed to flourish, I saw similar aberrations. This is wonder tainted strong with revulsion." This hints at the Hunter's previous encounters with Lifeblood/Plasmium, adding layers to the game's interconnected lore.
The Plasmium Phial stands as one of Hollow Knight: Silksong's most versatile and powerful tools. From its basic healing functionality to the advanced overdose mechanics, mastering this tool will significantly improve your chances of conquering Pharloom's challenges. Whether you're facing difficult bosses, exploring treacherous areas, or attempting challenge runs, the Plasmium Phial provides options and strategies that complement any playstyle.
Remember to complete both the Alchemist's Assistant and Advanced Alchemy quests to unlock the tool's full potential. With the Plasmium Gland upgrade, this tool transforms from a situational healing item into a core component of your arsenal. The journey through the Wormways may be dangerous, but the reward is well worth the effort.
As you continue your adventure through Pharloom, experiment with different Crest combinations, master the overdose timing, and discover your own strategies for maximizing this powerful tool. The Plasmium Phial isn't just a healing item – it's a game-changer that opens up entirely new approaches to Hollow Knight: Silksong's challenging gameplay.
For more Hollow Knight: Silksong guides, tips, and the latest updates, bookmark this page and join the vibrant community discussing strategies and discoveries. Happy hunting, and may your Plasmium reserves never run dry!