The Alchemist

The Alchemist is a faceless, mentioned only, character on the island. His current fate is unknown. May be The Collector, or his teacher, as the king gave the alchemist a wing of the castle to study the Panacea in order to cure the malaise, based upon what the collector says during his boss battle on a 5bc run.

Lore
Some soldiers were siding with the Alchemist and contesting the King's methods. In the Forgotten Sepulcher, one of those soldiers who was in direct contact with the Alchemist built a secret lab, presumably to do experiments related to the Malaise.
 * "I realize the risk I'm taking by writing this letter. The King's methods are getting us nowhere and the situation is deteriorating. We have to switch a more peaceful method immediately! I've spoken with the alchem..." - Letter found next to a clandestine lab

Sewers network
In the Sewers and the Ancient Sewers, the Alchemist was collecting mold and mushroom samples for his experiments. However, the increase in the numbers of revenants made his work increasingly difficult.
 * It is becoming increasingly difficult to collect mold samples in these sewers. There are too many revenants.

Promenade of the Condemned
In the Promenade of the Condemned, All species found in these areas seem changed. Was it the insects that spread the Malaise all over the island?
 * The character mentions that the Alchemist was very thorough upon inspecting the insects next to this grimoire.

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 worth killing so many people.
 * 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?
 * About the bodies next to the grimoire, the Beheaded mentions it's 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.

The Alchemist writes that people believe the sap flowing through the walls of the Sanctuary is responsible for the Malaise, by contaminating the sewer network. He also suggests that this same substance could be the solution to the epidemic. it is unclear if the substance is in fact the source of the Malaise or if it's only a rumor. What is sure is that the Alchemist 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. 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.
 * 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?
 * "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 that 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 waking up and the Darkness was making his work difficult, prompting him to leave this area.
 * "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.