thalmin
Retired game store owner
I wouldn’t say “never”. AD&D 1E had a wonderful Assassination chart. It’s primary purpose was for Assassins to get an instant kill. But a second use was for any character to maybe get an instant kill on a “held or helpless” opponant.D&D has never been set up to accommodate that sort of thing, unless you surround them with epic NPCs who would each on their own be able to take out the whole town.
I think you either ask the players to buy-in and narrate it, come up with some clunky house rule, or accept that this game isn’t designed to do that and focus on what the system is good at, which is heroic high fantasy.
Not the answer you were looking for, I know. But right tools for the right job, and all that. You’re trying to use a paintbrush to replace a sparkplug.
First the DM determined if the situation warranted use of the table. (I always also determined whether an attack roll was needed and if bonus to hit or advantage were in order). The Chart looked at attacker and target levels. The attacker then rolled on the chart. If successful, target(s) reduced to 0. If unsuccessful, but still scored a hit, apply damage as normal.
We only considered a well planned and executed ambush as worthy of the chart. A sleeping target wasn’t helpless.
For the something like the OP is asking about, I would tell the players of the possible outcomes. But also it is important to inform the players that this mechanic is in place for the game before they are targetted, so maybe they get to use it themselves.