Hollow Knight: Silksong | How to Get the Plasmium Phial

Here's a guide on how to get the Plasmium Phial in Hollow Knight: Silksong.

Game Guide by Imdeadfrfr on Sep 21, 2025

In Hollow Knight: Silksong, combat is wholly dependent on two things: how hard you can hit and how hard you can get hit. This can be changed by several factors; one of these is increasing the health you have. Plasmium Phials stand out as the best way to increase their masks.

Today, in this guide, I will help you find the Plasmium Phial.

Hollow Knight: Silksong, How to Get, the Plasmium Phial

What You Will Need

You will need the cling grip ability, which allows you to do wall jumps. Having the double jump ability also makes travel easier.

Hollow Knight: Silksong, How to Get, the Plasmium Phial

The Location of the Plasmium Phial

At first, you will need to make your way to the Wormways area, to the topmost section on the left. You will have to use the cling grip ability here to make it across the twisting caverns of Wormway. You can also find a bench there.

An easy way to travel through these passages is to use the dash ability whenever you come across the worms, which shoot through the roof and the ground, travelling vertically.

Hollow Knight: Silksong, How to Get, the Plasmium Phial

Getting the Plasmium Phials

After reaching this location, you have to interact with an NPC called Zylotol, who is a crazed alchemist experimenting on this substance known as plasmium.

To get the Plasmium Phial, you have to complete the Alchemist's Wish. In this quest, you have to find sacks of plasmium around the Wormways and collect them using a tool given to you by the Alchemist NPC.

One of these sacks can be found directly below this location, on the left of the passages. You have to drop down and move to the left; reaching a pit of spikes, you will have to wall jump over to the other side on the left and make your way down until you reach a room with a blue hue.

The second and last sack can be found near the crossroads between Wormway and Bone Bottom, where you have to enter, move to the left until the first drop you find, drop even lower, and move right until you reach a greenish patch reminiscent of Bone Bottom. Here you will find the second one.

For the last entrance, enter into the very next passage opening you find on the left of the area you are currently in.

Keep going left and wall jump up and enter another room. From here, you will have to make your way to the left all the way until you reach a very small platforming section of spikes, crossing which will reveal the plasmium sack.

After collecting the plasmium, simply return to the alchemist, and he will give you the plasmium phial.

Being Able to Replenish the Phials

Initially, you cannot refill or recraft the phials on your own, requiring you to come to the alchemist to buy the phials again for rosaries. To gain the ability, you need to complete another wish, which is the Advanced Alchemy Wish from the alchemist.

To complete this wish, you have to take the tool again from the alchemist and hunt down enemies infected by the plasmium and collect their blood.

These enemies can be found all throughout the Wormways, and to kill them, you just have to use the tool on them, which instantly kills them.

After killing and collecting all the required plasmium blood from the enemies, returning to the alchemist, you find him in a corrupted state, consumed by the experiments he had once overseen.

You give him the plasmium blood, and in turn, he gives you a plasmium gland, which now allows you to replenish the number of phials you have just by sitting on a bench.

Hollow Knight: Silksong, How to Get, the Plasmium Phial

The Application of the Plasmium Phials

As previously mentioned, the Plasmium phials are a way to increase your health; this is done by adding extra masks onto the masks Hornet already has. This causes the overall damage that a player can receive to increase.

This is especially helpful in the later stages of the game, such as in Act 2, where most enemies do 2 masks of damage. This is also extremely helpful for boss fights, as it increases the chances of you beating them, simply because you can take more hits.

Although it is good for scenarios like platforming, you only get a few extra hearts, which reset once you sit on a bench.

With the Architect Crest, this tool can be stepped up even further, as it allows you to replenish the number of phials without ever even needing to sit on a bench. This allows you to stack 8 extra hearts. Beyond which an interesting interaction takes place.

Also, check our Hollow Knight: Silksong Review and other guides below: