Hey there guys, I'm dming a campaign and at some point a while back the players picked up a merciful scythe. After our last session my rogue started asking me questions about how a non-lethal bladed weapon could work, and I wanted to get an opinion on that.
Can a merciful weapon puncture or sever body parts? If so, could it decapitate somebody and magically keep them alive, or is it incapable of actually cutting and just deals bludgeoning damage?
Slashing weapons have no restriction for non lethal damage as stated above. It is the same effect to deal NL with a mace, a club, a spear, or a scythe. Certain weapons are easier because of feats, Bludgeoner for one makes blunt weapons function with no issue.
If you are looking for flavor as to how it works, that’s always an issue I run into as well. It’s harder to describe how the 20 slashing or piercing dmg is not lethal.
There's this idea that nonlethal damage must be bludgeoning. That isn't how it works. Attacking nonlethally with a longsword still deals slashing damage--it's just nonlethal, presumably damaging less essential parts of the body or making shallow cuts. Attacking "with the flat of the blade" would be using the longsword as an improvised club.
Similarly, a +1 merciful longsword, when active, deals nonlethal slashing damage. A coup de grace with an active +1 merciful longsword would deal a whole lot of nonlethal damage and force the victim to make a Fortitude save to avoid immediate death. At that point, sure, cut off their head, etc. They're still dead.