What are the stages of Ceremorphosis?

Question

I wanted to slowly have one of my characters turn into a mind flayer, does anyone know the steps/stages in detail for ceremorphosis? I thought I had read it somewhere once but can't find it now, like skin becoming covered in slime... teeth slowly falling out, hair falling out, brain swelling, tentacles growing etc.

Answer 1

It's Pretty Vague

No source spells out anything more than the basic timeline of a week for ceremorphosis to be completed. Even older editions only lay out the pace at which the tadpole murders the host - in 2nd Edition, this was 1 hour (The Illithiad) while in 3rd Edition the process was a little kinder, taking as many hours as the lowest mental ability score of the victim (Lords of Madness).

...But We Can Infer

Thanks to the Baldur's Gate III announcement trailer, we can make some basic inferences; though the transformation depicted is considerably more aggressive (and involves more physical swelling than ceremorphosis should, considering it's a drain on the body's resources and reduces some components such as number of fingers), we see a few steps that can be clearly identified, in order:

• Disorientation and headaches
• Hallucinations
• Physical pain from the beginning of the transformation
• Transformation of the dietary tract (inferred from the pain without obvious physiological symptoms and dark-colored vomit)
• Loosening of/loss of teeth
• Integration of the tadpole's tendrils into the bony structure of the face causing distention of the jaw from the sphenoid
• Softening of cranial plates, swelling of tadpole's brain mass
• Atrophy of unsupported digits, development of webbing
• Hair loss (mucus likely deploys alongside or shortly after this as follicles, sebaceous glands, etc. are repurposed)
• Emergence of matured tentacles from the mouth

From here it skips ahead to completion; it should be noted that the mind flayers depicted here are somewhat different from conventional ones (i.e. the yellow-iris eyes, rather than the dead white eyes they should have) and are suggested to be using a process to significantly accelerate ceremorphosis, so this is hardly the be-all, end-all. Given the aggressive infestation of the tadpole into the brainstem, the victim should also be quite dead and not feeling any kind of pain well before any meaningful tissue transformation becomes apparent.

Further Notes

From the adventure Divisions of the Mind (Dungeon 81) we discover the effects of incomplete ceremorphosis in the form of Lazat Lan, who appears to be human but is an illithid in both mind (including psionic abilities) and dietary needs, complicated by his human physiology. This suggests that the changes to the digestive tract come much earlier than external physiological changes, and I would hazard that a deficiency with the tadpole's tentacles prevented their embedding in the bones of the skull and secretion of the necessary mutagenic enzymes to catalyze tissue transformation and growth. Going by his ragged appearance (and the fact that he was being kept prisoner), it's likely that the internal transformation is instructed by enzymes passed down through the brainstem and through neurological changes from the tadpole's brain connecting to the spinal column, but the external changes require successful tentacle embedding.

In Conclusion

We've got little apart from conjecture, the trailer, and old editions to go on, but I hope you find it useful as a starting point.

Answer 2

Volo's Guide to Monsters has the only detail on the process I could find (from an official source). Page 72 says

Over the course of a week, the humanoid body changes form, and a new Mind Flayer comes into being.

Not a lot to go on so I guess you have artistic license to describe the process in whatever way you desire.

This fandom site references older resources from previous editions that you maybe able to source for further information.