Mafia 90. The Tale of Oldforest.

I'm afraid to imagine how GMs come up with these hints. Do they just pick any word they like and start guessing?

In reality, the hints vary in difficulty. For example, GK gave a hint in his game, and it was a hint for all the hints!
We have hints related to quests; in GK's game, there were musical instruments, and the player Leizket had a violin. GK gave the hint:

And again, a brutal murder. This morning, in one of the office premises in the city center, the body of
alkamfell
was found. Despite the horrific condition of the body, it was quickly identified. The murder weapon was also found nearby – an axe from the Magic company with the inventory code MHNCH TUDB NVII TITV TVII MNNI. Forensic experts are currently working on it.
(c)
Ask solved this hint; MHNCH TUDB NVII TITV MNNI are the first letters of the lines from Gumilev's poem "волшебная скрипка" (magical violin)
http://www.gumilev.ru/verses/204/
(an axe from the Magic company)
So, Leiza was immediately convicted. It was an undeniable solution