D&D 5E How to run a successful "poisoned NPC" scene in 5e?

[Morrus]

I am interesting in how you introduced this houserule to your group. Or if you didn't do the introduction, how it was done?

Just mentioned it. It wasn’t an event. We’ve been using it for years.

 

[Istbor]

Just mentioned it. It wasn’t an event. We’ve been using it for years.

I had a feeling you would say that. It just seems like such a "Why didn't I think of that" idea. Well thanks.

 

[Paul Farquhar]

I have just replayed the start of Neverwinter Nights: Shadows of Udrentide, and that uses exactly this plot device. At the start your mentor is struck with a poisoned dagger. A high level cleric arrives and tries to magically heal him. She cannot heal him because he has been poisoned with "magically altered asp venom". She suggests trying a herbal remedy of Tressym Tongue, Helmhorn berries and charcoal. Just off to fetch them now.

 

[Lakesidefantasy]

In Curse of the Crimson Throne they killed an important person with a poison that acted like a disease (or vice versa). By the time they figured it out it was too late.