This post extrapolates on an encounter in the early areas of the Sunless Citadel for DnD 5th Edition as found in Tales From the Yawning Portal.
There are SPOILERS below for the SUNLESS CITADEL below!
You have been warned.
In Room 12 the players encounter the Tomb of a Failed Dragonpriest, who was imprisoned for delving into profane magic and turning himself into a troll.
The Dragonpriest, Agnon Sa'Tok, came into possession of a blasphemous scroll left behind by a troll mercenary during the Dragon Cult's reign in the Citadel. The scroll, written in Undercommon, briefly described the Pantheons of the Giants, but focused mostly upon practices and rites to worship Vaprak the Destroyer. At first, Agnon found the work amusing at most, but he could not keep it out of his mind. As he began to study it, he discovered a hidden cypher that allowed him to unlock deeper secrets about the giant deity. Eventually, he became completely obsessed with the scroll and even began communicating with Vaprak, who offered him a pact, giving Agnon fiendish power in exchange for Vaprak's patronage.
Agnon, at this point had completely turned his back on the worship of Tiamat and failed to notice the whispers of his fellow Dragonpriests that had been circulating through the Citadel. One of his bitter rivals, finally brought to his odd behavior to their Superior's attention, in a bid to replace him.
Agnon had just finished Vaprak's final task to gain the god's Patronage, which transformed him into a troll, when the Dragon Cult acted, subduing him and encasing him, still alive, in the sarcophagus of Room 12.
For the Encounter, the DM could allow the Dragonpriest to use the Eldritch Blast Cantrip.
In Room 11, not only is the inscription in place to warn others about Agnon Sa'Tok's transgression, but on a shelf, just below the runes is the original scroll that he had found and his journal containing instructions on how to make contact with Vaprak the Destroyer and eventually gain the deity's Patronage as a Fiendish Pact Warlock, in Giant.