Shadows can kill if they drain your strength.

Probably something like kobolds for dex, due to their heavy use of traps. Strength could be something doing a lot of potentially breakable grapple checks. Con could be a lot of things, probably something poisonous. Wis could be a lot of things too, but for fun let's say something that can kill you quickly if you fail to notice it in time, like rot grubs or green slime. Cha could be a court magistrate who wants you executed unless you can talk your way out of it. lol

Mostly basing these off the 3.5 ruleset incidentally. Older editions used to be a lot more deadly, overall.

Banshee for con? Their wail instakill (dc13) mechanic is bad enough that I've never run banshees against my players

fully agree on intellect devourers

one of my favorite characters ever got killed by one right in the classic brain eating way.

he had 5 int, gotta love rolling for stats