I Really Don't Want to Learn Forbidden Spells - Ch. 68

[MangaDex]

 

[Kaarme]

Yeah, like one of the demon lords. It would be a pretty nice trick to keep feeding the black market with legit potions for a while, creating a stable demand and pool of satisfied customers, but then suddenly switch the contents of the potions to a horrifying type of poison that will mutate the users into darkness power monsters. Preferably the transformation should happen with a delay so that the users would keep using it, ignorant of the danger and not alerted too soon by news of the first users getting transformed.