This is a list of the NPCs in Red Dead Redemption 2 that can kill the player in one hit.
As a disclaimer, I understand that the night folk only sometimes kill the player in one hit, and that it doesn't happen all the time. However, they are listed as one of the 4 NPCs that kill you in one hit according to the Red Dead wiki.
0:00 Intro
0:19 Sheriff Freeman
0:55 The Hermit
1:59 Night Folk
2:56 Vampire
4:33 Outro