My INT theory is sort of busted. I leved a cleric up to 100 without increasing a single point into INT or equipping any INT items. The NPC wasnāt there for me at lvl 100.
I then did mage tower chain with all side quests, still not raising a single point into INT. got to level 120 ish. Still no NPC.
Went into starving demon way and did the quests on that map and the next one. Still not equipping any INT item other than the necklace of gluttony. Went to check NPC and he was there.
The trigger could still be something like āequipping any item that increases any stat past Xā but that sounds sort of vague.
The NPC says he once buried a revelator. The trigger could be character deaths too.