Dungeons and Dragons, and the 'Stealth Kill'.

I recently stumbled on a post on reddit where someone was complaining about how difficult (or indeed, impossible) it is, in 3.X, to stealth-kill a character. As written the only way to do this is with levels in the prestige class Assassin.

Once a couple of hit-dice are involved, even a Rogue will struggle to do enough damage (9th level Rogue does ~6d6 damage on a Sneak Attack vs the 9d10 and change hit-points of an equivalent level NPC Warrior)

This is a much smaller issue, under the Wound Point system I use, but given my love of games like Shadowrun - why shouldn't I consider this problem... So I propose the following.

"A character who wishes to sneak behind an unaware victim - with the intent of dropping them during the surprise round - makes a Stealth check against the victim's passive Perception DC. A success allows the skulker to score an automatic critical threat - an attack roll is still made to confirm it, noting that the victim is helpless. Failure indicates that the victim has become aware and turns to face their would be murderer - roll for initiative."

The Assassin, from the 3.5e DMG

This is similar to the mechanic for a Coup De Grace, however as written a coup de grace attack must be a full round action, while the surprise round lasts only long enough for a standard action at most.

Under my house rules, against plot-bearing NPCs this has the potential to be disruptive - as 20 damage is enough to deplete near-any humanoid's Wound Points. But frankly, if the Mundane Badass of the party sneaks up behind the Big Bad to drop him in one - and fail for no other reason than hitpoint inflation; when the Wizard has an inventory of Save Or Lose spells that would be little worse... They're going to feel cheated.

Under the RAW 3.X rules, the Rogue would still only be looking at (with +1 Flaming Shortsword) 8d6 against 9d10. The Warrior would survive more than half the time. As a Coup De Grace, 8d6 yields an average Fort vs Death DC of 38. A level 9 Warrior has a Base Fort of +6, we'll assume a Con of 16 for +9 total, a 90% chance of death - which compares too favourably against the Wizard's best DC of 15+Int - which is why I would not allow a full Coup De Grace.

This probably doesn't lie too far from what is desired of the system. The main issue does seem to be that Perception becomes an even bigger Godstat in Pathfinder. Request for comments guys!