The Alchemist

The Alchemist is an unseen character on the island. He intended to develop a cure for the Malaise, though his efforts appeared to all be unsuccessful.

Lore
The Alchemist is implied to be unpopular throughout the island’s hierarchy, as the Giant and the Hand of the King both agreed "nobody liked the Alchemist".

During the Malaise epidemic, the Alchemist used scientific means to find a cure for the Malaise, as well the source.

The Alchemist gathered research from all over the island to learn the origin of the malaise. He also conducted many experiments to combat the malaise, using corpses or volunteering villagers for his work.

His research took him to a sanctuary beneath the village. Some believed the liquid sap running through the walls of the sanctuary could've been contaminating the sewer network and thus causing the malaise. With this knowledge, the Alchemist began experimenting with the sap. Over time, he learned mutations in the infected slowed down when submerged in a solution of the sap.

However, the sap provided unpredictable results on the bones of corpses. The Alchemist reflects on whether the King’s methods were worth killing so many people.

Within the Undying Shores, the Apostates provide him with valuable research; he remarks there may be another way to endure the malaise.

Some soldiers had sided with the Alchemist against the King. In either Ossuary or Sepulcher, one of those soldiers, who were in direct contact with the Alchemist, built a secret lab, presumably to do experiments related to the Malaise. Furthermore, a soldier's note in the Undying Shores mentions the Alchemist, wondering if he find a remedy from the scrolls and book gathered from the Apostates hideout.

Stilt Village
In the village, the Alchemist had set up a laboratory, dedicated to curing volunteers of the malaise, he reports that the essence of bupleurum seems to relieve symptoms.
 * "The treatment administered to the latest volunteers seems to be producing results. They are still coughing but they are vomiting much less. Or less blood, in any case. Am I on the right track?"

Sewers network
In the Toxic Sewers and Ancient Sewers, the Alchemist was collecting mold and mushroom samples for his experiments. However, the undead creatures were getting in the way and so he presumably ceased his attempts there.
 * "It is becoming increasingly difficult to collect mold samples in these sewers. There are too many revenants."

Promenade of the Condemned
Inside the tower, the Beheaded mentions that the Alchemist was very "thorough" upon inspecting the portraits of insects next to the grimoire.
 * "All species found in these areas seem changed. Was it the insects that spread the Malaise all over the island?"

Ossuary
The Alchemist was applying a substance found in the Sanctuary on bones from corpses, likely executed prisoners. The substance's effects were unpredictable and the Alchemist reflects whether his experiments are worthy or the mass murders from the King are more effective.
 * "The sanctuary substance produces unpredictable results on the bones I've collected here. All these bodies... All these lives. At the end of the day perhaps the King is right?"

Referring to the bodies next to the grimoire, the Beheaded makes the remark:
 * "Hard to say whether these bodies were infected. But one thing is for sure: their skin melted like old cheese in the sun."

Slumbering Sanctuary
The Sanctuary seems to have been especially important to the Alchemist's research. It's the only biome that contains two different Grimoires.

According to one of his writings, people believe the sap flowing through the walls of the Sanctuary is responsible for the Malaise, by contaminating the sewer network. He also hypothesizes that as a potential cure. He harvested and used this substance as part of a treatment for the infection, as indicated by the Grimoires of the Ossuary and the Clock Tower.
 * "Some say the sap that runs through the walls is flowing into the sewer network and causing the Malaise. But perhaps the problem can also be the solution?"

In another Grimoire, the Alchemist references the Time Keeper's efforts to combat the Malaise. He implies that she is manipulating time to contain the Malaise, but that her spell cannot contain it forever.
 * "Time is running out... literally. With all due respect, she cannot contain the Malaise forever"

Clock Tower
In the Clock Tower and the Castle, a grimoire reports that the Alchemist found a formulation from the sanctuary's sap slows the down the mutagenic effects of the Malaise.
 * "The bodies immersed in the latest solution are changing less quickly. I must extract the essence of this solution and apply it to other volunteers"

Forgotten Sepulcher
The Alchemist was also researching the Malaise in the Forgotten Sepulcher, but the bodies kept resurrecting themselves and the Darkness was making his work difficult for reasons yet to be specified. These prompted him to leave.
 * "The bodies have woken up again. And this darkness... I can no longer continue my experiments on the Malaise here."

High Peak Castle
The Alchemist was attempting to cross human bodies with plant essences, which gave rise to the hybrid found in the Castle's green Elite Room.

Additionally, there is a lab in the Castle destroyed by the King's loyalists, all of which criticise the Alchemist's efforts for creating a cure, and that isolation is more effective.

Cavern
The Alchemist was using the crystals mined in the cavern in his experiments to slow the Malaise's infection, as evidenced by a body immersed in a crystal solution next to his grimoire.
 * "We can do more with those crystals than sell them, I'm sure of that. Using them on corpses doesn't do anything for now, but I have to keep going!"

Undying Shores
Within the Undying Shores, a room with a desk and the Alchemist's grimoire can be found, the Alchemist notes the Apostates provide him with valuable research; he remarks there may be another way to endure the malaise.
 * "The Apostates' research on death and cellular decay were far more advanced than what I've seen elsewhere.... They seem to endure better than the rest of the island. We shared knowledge, and they handed me some precious samples. There may be another way to endure the Malaise..."