É um processo conhecido como ceremorfose.
Vários artigos sobre o Portão de Baldur III trailer indica que o processo descrito é de fato ceremorfose.
Rock Paper Shotgun toca nele:
They call it Ceremorphosis. The excruciating seven day process by which a humanoid might transform into a Mind Flayer. Stick one illithid tadpole in the brain and one week later you’ve got an octopus for a head and a craving for more grey matter. [...]
Before we chat specifics: that reveal! Blimey. Ceremorphosis might be the inspiration, but when crafting a 90 second teaser trailer you’ve got step on the gas a bit, so the process is accelerated. A week of suffering becomes a frankly horrendous slice of Cronenbergian body-shattering that is so gnarly the uncut version of the teaser was not shown at today’s Stadia announcement. I know Google want us to give their streaming tech a thumbs up, but not when that thumb is being snapped 90 degrees by a mind maggot.
É confirmado pelos próprios desenvolvedores em este artigo da GameSpot, em entrevista ao chefe da Larian Studios, Swen Vincke:
For anyone who's not familiar with Baldur's Gate, as you said before there are people that are new to this franchise, can you kind of break down what we're seeing in the teaser that will catch us up and get us ready for Baldur's Gate 3?
[...] There's dead bodies everywhere and then something's happening to this knight and he's actually undergoing a version of what we would call accelerated ceremorphosis, which is basically a way of reproduction that these creatures called the mind flayers have.
They stick a tadpole in people's heads, that tadpole grows, and then it turns a human being or any humanoid being into a mind flayers and these are the guys you may know from Stranger Things, maybe. They're these psyonic creatures with tentacles and very intelligent but they're hive creatures. They have elder brains that command them.
They used to have an incredible empire called the Mind Flayer Empire but things went wrong, so they've been in hiding ever since in a place called The Underdark, which is like the deep underground of this world of Forgotten Realms. Somehow, they've managed to get people into Baldur's Gate that are turning into mind flayers and you see some shots where they're flying in the distance, so it's an invasion of mind flayers, too.
Você pode encontrar mais informações sobre o processo em o artigo wiki Forgotten Realms sobre ceremorfose, que cita livros de edições anteriores e também Guia de Monstros de Volo.
O co-fundador da Larian Studios, Swen Vincke, também recria brincando a reunião com Mike Mearls e Nathan Stewart em o primeiro vídeo de atualização da comunidade dos Larian Studios para Baldur's Gate 3. Nele, eles discutem o processo de ceremorfose.