I'm attempting to design a garrote weapon that a PC could use – by player request. And I was wondering if any of the ENWorld brain trust had experience adapting garrotes to 5e? How did it go? What worked and what didn't work?
That was the Tl;dr version of my question. I realize that implementing the garrote specifically is a contentious issue, where the usual consensus is "it's really hard." And yet, here I am trying.
So your player wants to be able to use a garrote to dispatch enemies, correct?
Is there anything else they want to do with this weapon? It isn't something you can easily use in a cinematic/heroic D&D fight. If the player wants a means to silently remove an enemy, why not just tie it to the stealth mechanic? If the stealth roll is high enough, the player can dispatch the sentry with the garrote. A rogue character who wants to eliminate a guard would love this. But it isn't going to bother with grapple rules or even needing weapon damage. If the player wants to use a garrote in a traditional fight, I would just use a dagger or short sword and re-flavor it. We have characters who can punch a troll for damage, this isn't breaking physics or immersion.
If you are worried about stealth being boosted into the stratosphere with buffs, allow the other guards to roll with advantage vs the stealth roll to hear any noise from resisting. And make it take time. The PC super rogue can definitely silently dispatch everyone, but it takes time and someone will notice one of the bodies, eventually.