[RPG] Ending combat: should I “kill” monsters prematurely

I think the best way to do it is to benchmark an MM3 monster of the same level and role and do some comparisons. Simply updating damage on the basic attack is a quick solution, but consider other effects. I really do think there's more than adjusting some numbers here.

Here's a Harpy Screecher.

It's from an early period of D&D4 and has those same standards. Presumably, it needs to be updated.

Here's an MM3 level 9 controller.

From what you can see, the stats (hp, defenses, to-hit..) are mostly comparable, except for the damage from that basic attack- which is about 8 (average) from the Harpy and 15 (average) from the Meenlock Stalker. I think the Stalker has a more powerful encounter power (the Horrid Link ability, vice Acerak's Slave), but otherwise the Harpy's screechy pull and slide powers and the Meenlocks dazing and quasi-dominating powers are comparable.

If you really wanted to beef up the Screecher I might add some damage to her basic attack, but it might be even better to give her something like a minor action rechargeable encounter power- perhaps something that chains off of slide or daze, minor action, rechargeable on a 4-6. It doesn't even have to do damage. A fortitude attack that gives a character Vulnerability to Thunder damage or reduced defense against charm attacks.. would also be great.

Causing a vulnerability does the increased damage you want, and creates a more interesting status effect. Another alternate solution- instead of doubling creature damage, consider giving the creature an attack that allows for two basic attacks.

Take a look at Break & Enter by Emerald Press. I have a copy and it provides an excellent framework for stealth encounters complete with stealth kills and ways the entire party can participate. (Link to driveThruPress)

It offers a way of calculating "unaware HP" that only enemies not aware of the players' presences have, and adjudicating attacks against them. It's certainly worth trying if you find your players wanting to do quite a lot of sneaking, as the default rules do not support that kind of play.

Without going into detail about the excellent stealth mechanics, guards going on their rounds and so on, we have selected excerpts:

To understand the function of a stealth encounter, we must first explore its need. All heroes find themselves between a rock and hard place at some point in their travels. Your dailies are used up, most of you have expended your second wind, and you’ve wound up knee deep in enemy territory. Taking an extended rest is not possible until you find a haven somewhere within the dragon’s lair away from the uncounted demon minions guarding that immense treasure and patrolling the winding caverns. Up ahead, a pair of drakes feed on their latest catch. Their backs are turned to you, their snouts engorging on the innards of a poor villager. According to the map, you’re mere feet away from the guardhouse and the door just behind those beasts is the only means to access the inner sanctum of the lair, but your party is weak from your previous efforts. You need to take out those drakes quickly and quietly.

Cue the stealth encounter.

Stealth encounters allow the GM to replace an existing combat sequence with subterfuge and surprise without altering the build and composition of the player charac- ters. By sneaking up on the unsuspecting drakes in the example above, the PCs can eliminate them quickly without any unwanted attention from other targets nearby. They use skill checks (just as they would in a skill challenge) to create combat results (as with a combat encounter). More importantly, running a stealth encounter allows the GM the opportunity to continue large portions of an adventure with few modifications until the heroes find themselves in a favorable situation or it is no longer feasible to creep and skulk. Once the PCs get past the drakes in the paragraph above, they can continue sneaking through the lair until they have been spotted and an alarm sounds or they reach the dragon himself and engage in open combat.

...

Unaware HP is a mob's Constitution modifier (minimum 1) with more if they're large, and wisdom modifier if they're elite or solo. Standard creating a mob calculations for everything else. (page 24-25)

Looking at how this plays out, the emphasis is on quiet, silent, attacks... rather than big flashy attacks that make noise, have arrows passing through visual range, or have showy magic. Because an elite or solo can be dropped by any character in a round, a scene's tension is not in 5 rounds of combat, but a slow build over many rounds of a successful sneak to get to that point. When considered over average numbers of rolls, the amount of time a character spends getting in position, cleaning up after the body, and the number of stealth checks necessary more than makes up for the quite neat consequence of dropping the solo in one hit if everything goes according to plan.