How to Find All Three Plasmium by Completing and Solving in Hollow Knight: Silksong

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The Wormways in Hollow Knight: Silksong are not safe places to linger—they are crumbling and filled with danger. However, daring explorers who risk their silk might unlock secrets to longer life by discovering the mysterious substance called plasmium.

If you encounter the Alchemist inside the tight tunnels of the Wormways, he will consider you his assistant in studying this strange material. With the proper tools, you can harvest the blue liquid similar to Lifeblood and gain the power it offers.

How to Start the Alchemist’s Assistant Quest

To talk with the Alchemist and start this quest, you must have unlocked the Wormways. That requires the Simple Key, which you can find in one of two places:

Purchased from Pebb for 500 Rosary
Dropped by a tough enemy at the top of Sinner’s Road

The first method is usually quicker, but either method works. Once you have the key, use it to open the Wormways door at the top left part of the Mosslands.

Note: If you’ve already reached Sinner’s Road before getting the key, it’s better to cross through Shellwood and enter from the top Wormways entrance instead of wasting the key.

Once inside, the Alchemist is located at the top center of the map. To reach him, you need the Cling Grip ability, which requires defeating Sister Splinter in Shellwood and claiming Cling Grip from the Herrah statue at the top of Shellwood.

Getting the Cling Grip

If you don’t have Cling Grip yet:

Go to Shellwood
Defeat Sister Splinter
Claim Cling Grip from the Herrah statue

With Cling Grip, you can climb walls to reach the Alchemist.

Tip: It’s best to wait until you’ve saved the residents of Bellhart to get the Needolin ability. This gives you deeper insight into your quest and makes the journey more rewarding.

Inside the Wormways and Finding the Plasmium

Once inside, head to the top middle of the area where the Alchemist is. From there, descend into the main Wormways area, taking a slight left past the falling worms, climbing a small hill, and then floating down toward a blue light to find a hidden alcove containing plasmium.

There are three plasmium deposits:

Two are located at the bottom of the Wormways
The third is along the way to the lower depths

Each plasmium looks like a bright blue flower filled with liquid. To collect it, use your trap button and hold it down until the vial charges, then release to absorb the plasmium.

Where to Find Each Plasmium

First Plasmium
This one is closest to the Alchemist but less obvious. After leaving his room, go down into the main Wormways, then:

Take a slight left, drop past the worms
Climb a small hill on the left
Float down toward a blue light and alcove on the right, where the plasmium is nestled

Second Plasmium
From the Alchemist’s room, go downward through two rooms, staying to the right. Navigate through dark corridors, and when moss appears, head right. Follow the blue light to find the plasmium hidden in moss.
Third Plasmium
From the second deposit, aim for the bottom left. Head up and left, avoiding falling worms, go through a narrow entrance, dash across a room with worms, and descend a wall. Break the false wall on your left to reach the final plasmium, which is tucked into a shadowy alcove at the bottom.

Note: Exploring the area thoroughly is recommended, as a deceased pilgrim with a Memory Locket is hidden here.

Bonus: Finding the Last Assistant

From the third plasmium, jump across spikes to a ledge. Behind a shadowed breakable wall on the left, you’ll find a large chamber containing the previous assistant of the Alchemist, now overgrown with plasmium or lifeblood—no reward is given, but talking to this assistant unlocks special dialogue with Zylotol.

Rewards for Completing This Task

Returning the plasmium to Zylotol grants you a new charm: the Plasmium Vial. This trap item, when used, temporarily grants a blue mask of health. It doesn’t consume scrap, holds 20 charges, and can be used up to three times per rest. Although masks disappear when resting at a bench, its utility in tight situations makes it invaluable.

Special Effect: If you have the Pollip Pouch charm equipped, the Plasmium Vial will instead grant a purple mask, which bursts into venom when it expires, damaging nearby enemies—adding a strategic twist to its use.