Start of Turn triggered saving throw

I'm trying to trigger a popup in chat for a saving throw  at the start of a characters turn if they are in an aura. Specifically this one from the Nightwalker: Any creature that starts its turn within 30 feet of the nightwalker must succeed on a DC 21 Constitution saving throw or take 21 (6d6) necrotic damage. Undead are immune to this aura. I've seen some things that come close, but can't wrap my head around how to get it all working.  Thanks!

This sounds like it can be done with a combination of ScriptCards, Fetch, and OnMyTurn . OnMyTurn can trigger a ScriptCard on a character's turn that will look at the distance between the two tokens and then do the saving throw and damage if applicable. You'll need Fetch to get the token ids for the comparison.

Ha! I've been a Pro user long enough to know what all those things are... but what you are suggesting is way over my head at the moment!  Are there any good examples you can think of as a starting point? Zone of Truth spell is similar-ish if someone has that kicking around ;)

Hi Jeremy! Most any programmatic solution is going to take a similar amount of prep work. I'm assuming this is a one-off encounter? In which case, I suggest that your time would be better spent just remembering to ask for the save at the beginning of each turn for that one encounter.

Wait. You mean I'm not supposed to spend an hour automating a task I'll only use like 4 times? That doesn't sound right.