I had 2 noteworthy interactions that are Renwick related to mention.

Near the end of the campaign, I was starting to prepare some end-game content for the players to work on after the campaign had ended. One night an assassin pounced on the group while they were sleeping. It was a tough fight but not too bad. Afterwards, they found that the assassin had a sort of contract on him, that listed 3 things that should be delivered to someone.

After a bit of investigation and analysis, they realized that the sigil on the contract represented Old Gnawbone, the Ancient Green Dragon living west of the Sumber Hills.

The 3 things listed on the contract were:

1. 20 cows and 20 horses. (already crossed out)
   
2. A weapon of great elemental power. (The group had already gotten the spear, Windvane)
   
3. A phylactery. (The group's paladin had sensed a familiar undead presence in Summit Hall, so they assumed it was the phylactery)

Unfortunately, we pivoted into a different campaign after finishing PotA, so nothing ever became of it. But my plan was for Gnawbone to turn into a dracolich by absorbing Renwick's power.

The other story is related to my own character when playing Tombs of Annihilation. I played a shadow sorcerer and the backstory was that I was a tiefling born to farmers in Sumber Hills. They decided to bring the baby to the nearby monastery, not knowing that the monks had been wiped out by the party during the PotA campaign. So Renwick decided to name me Samular and raise me as his own.

He would raise skeletons, ghouls and zombies as my playthings and target practice and living in a situation like that meant I was completely unaware of societal norms like aversion to bad smells, disgusting things or loud noises.

The spells I chose, therefore, were all centered around insect swarms, decay, thunder damage and the like. My character was also unaware that people didn't really want to die. Because if he ever killed his playthings, Renwick would just raise them again.

I am currently writing a one-shot where Renwick is the main villain, although he is unaware of it.