The problem with the Helpless Defender rule (not the CdG) is that all it does is give you an automatic hit.
In D&D terms, a dagger to the throat, even with an automatic hit, is not that scary starting at Level 2! 1d4 + STR mod damage.
You know you'll survive it.
I'm trying to take that certainty out of the equation.
I think there are some misunderstandings here.
First, the definition of a Helpless Defender does not provide an automatic hit using a regular attack. The automatic hit is only if one is using a
coup de grace.
The difference between using a regular attack and a
coup de grace (besides whether it's an automatic hit or not, and the damage dealt), is that the regular attack is a Standard Action and the
coup de grace is a Full Round Action.
If the Regular Attack is used, an attack roll is made against the target. If using a melee weapon, the target has a -4 penalty to AC, and their Dexterity is considered zero (-5 Dex Bonus)...for a total of -9 to the targets AC. If a ranged weapon is used, there is no -4 penalty to AC (so only the -5 for Dex).
If the
coup de grace is used (the Full Round Action), then it's an automatic hit, which is treated as an automatic crit. So, in the case of a dagger, the damage would be (1d4 x 2) + Modifiers (not just 1d4 + Modifiers).
Though I know, that's still not very much damage. However, coup de grace goes on to say that if the target survives the damage (which they likely do), they then have to make a Save vs. Fortitude at DC10 + damage dealt, or immediately die (reduce to -10 Hit Points).
That save though isn't very difficult as one goes up in levels either.
As a houserule, I'd suggest beefing up the
coup de grace. Maybe like this:
In a situation where you already have the target in a helpless position (got the drop on them), I'd let
coup de grace be an immediate action (reaction). Or, if that seems too powerful, allow opposing initiative rolls to see if the target can move quicker (to interpose a hand, shift enough to avoid a critical wound, etc.). If opposed initiative is used, then success by the target reduces the attack to a regular attack rather than a coup de grace, but at the same penalties as for a helpless defender (they got the drop on you, no matter what you're getting cut!).
Then, change the damage to not just a crit, but a crit with maximum damage (no matter what) - and add the attackers level or BAB to the Save DC.
Now it's got some teeth!
Man, what are you missing here.. a CdG can be used against *ANY* helpless defender that is susceptible to crits and this applies to "anyone at your mercy".
If you have a dagger to their throat and are a hairs breadth from slicing it it's a fair bet to say they're at your mercy.
So why the hell we need anything else is something *I* am not grasping.
The problem is that the rules are a tad vague on what exactly
"at your mercy" means. I believe it's the same thing that you believe it is, but not all DM's or Players interpret it this way.
For Water Bob's purposes, I'd just add a houserule for his games, and make sure the players know upfront, that
"got the drop on you" equals "
at their mercy".
