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The Plasmium Phial is one of the best tools in Hollow Knight: Silksong. This tool has 20 charges and can be used to boost your health beyond the maximum. You can inject yourself up to three additional times before a big fight, giving you a big early advantage, and you can continue to top-up your health after that. Initially, the Plasmium Phial has a big drawback because you’ll need to return to a specific character for refills, but later you’ll be able to earn an upgrade where Plasmium Phials can be restored at any bench location.
This is basically the only healing item in Silksong. Its best feature is the ability to add masks to your maximum temporarily, and being able to heal anytime, even when your silk isn’t full. The obvious drawback is that the Plasmium Phial only heals one mask per use, so it’s much slower than your standard binding technique for healing. But sometimes the difference between life and death is a single mask.
How To Get The Plasmium Phial Tool
To unlock the Plasmium Phial, go to the Wormways area. 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. Learn where to find a Simple Key here.
You’ll find a workshop in the Wormways with an NPC called Alchemist Zylotol. Talk to him to begin the “Alchemist’s Assistant” quest. For this quest, you’ll need to find three Plasmium locations in the Wormways. Plasmium gives off a faint blue glow.
- Plasmium #1: The first Plasmium is located in the maze of tunnels below Alchemist Zylotol’s room in the Wormways.
- Plasmium #2: In the maze of chambers at the southwest corner of the Wormways.
- Plasmium #3: 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. Bring the extracted essence to Alchemist Zylotol to complete the quest and earn the Plasmium Phial.
This powerful tool allows you to heal +3 above your maximum health and heal lost health. The blue masks are temporary and will disappear after resting at a bench. You’ll have 20 charges with this tool, and initially the plasmium can only be restored by talking to Alchemist Zylotol. To upgrade the Plasmium Phial, you’ll need to progress deeper.
How To Get The Plasmium Phial 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. Search the Wormways for enemies that glow blue and use the Needle Phial to collect Plasmified Blood.
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 makes the Plasmium Phial much, much easier to use.
This also allows you to use a secret function of the Plasmium Phial. 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. Instead of healing normally with binding, your health will slowly restore itself. Using Bind will heal only 1 mask in this state, so it isn’t a pure net positive. This Plasmium poisoning effect is cured if Hornet rests at any bench.
