In the Baldur's Gate III announcement trailer, we can see what seems to be a human be transformed into a Mind Flayer.
What is happening there? Are Mind Flayers created by transforming other creatures? I thought Mind Flayers only created Intellect Devourers, as written in the D&D 5E description, but not other Mind Flayers.
Unless it is more basically a polymorphism spell at hand?
Best Answer
It is a process known as ceremorphosis.
Several articles about the Baldur's Gate III trailer indicate that the depicted process is indeed ceremorphosis.
Rock Paper Shotgun touches on it:
It's confirmed by the devs themselves in this GameSpot article, in an interview with Larian Studios head Swen Vincke:
You can find more information about the process in the Forgotten Realms wiki article on ceremorphosis, which cites books from past editions as well as Volo's Guide to Monsters.
Larian Studios co-founder Swen Vincke also jokingly recreates the meeting with Mike Mearls and Nathan Stewart in the first Community Update video by Larian Studios for Baldur's Gate 3. In it, they do discuss the process of ceremorphosis.