[3.5] Skill checks to Sneak attack the unsneakable

[Cicciograna]

One of the major hassles for Rogues is that there are certain creatures - undead, constructs, elementals, oozes, plants, and incorporeal creatures - that are immune to sneak attack, since, according to SRD, they "lack vital areas to attack". This sucks.

While obviously such creatures lack vital areas, I fail to see why they couldn't have weak spots, places that, if hit, would really hurt. The charm is to know where these spots are; so I propose this House rule: prior to making a SA, by making an appropriate Skill check as a swift action to determine the weak spot of one of these creatures, the Rogue is able to SA them.
The DC for every check would be HD of the target creature.

Undead: Heal or Knowledge (Religion);
Constructs: Disable Device or Knowledge (Arcana);
Oozes: Knowledge (Dungeoneering);
Plants: Survival or Knowledge (Nature);
Incorporeal creatures: Spot or Knowledge (Arcana);
Elementals: Knowledge (the Planes).

PEACH.

[Curmudgeon]

While this is an admirable idea, I think you've over-reached. Instead of making the skill check a swift action, I suggest it should require a move action instead. This is consistent with the way Spot and Listen checks, to try to perceive things that aren't apparent initially, work.

Trying to hear something you failed to hear previously is a move action.

Trying to spot something you failed to see previously is a move action.

This change would impose a real tactical cost on the Rogue, whereas a swift action is for most purposes "free". You can always change the time requirement with an additional resource, along the lines of the Quick Reconnoiter feat (grants 1 Listen and 1 Spot check each round as free actions).

[Snake-Aes]

Change the reference, and you'll have to adjust it the other way around. Knowledge Devotion doesn't take actions and a single check lasts the entire combat.

[Koury]

Change the reference, and you'll have to adjust it the other way around. Knowledge Devotion doesn't take actions and a single check lasts the entire combat.

Of course, Knowledge Devotion has the same cost Curmudgeon suggested. A feat.

[pasko77]

The DC for every check would be HD of the target creature.

HD + 10, I suppose, or it would be autosuccess.
Maybe 10 + HD/2 if it scales too fast.

Anyway, the idea is great!

[Jack_Simth]

The DC for every check would be HD of the target creature.

Not a bad idea, inherently, but that's a rather low DC. Standard DC's for recognizing a critter are 10+HD.

Of course, if your primary intent is to simply enable the rogue, that aspect works, but might as well say it straight-out.

Undead: Heal or Knowledge (Arcana);
Constructs: Disable Device or Knowledge (Arcana);
Oozes: Knowledge (Dungeoneering);
Plants: Survival or Knowledge (Nature);
Incorporeal creatures: Spot or Knowledge (Arcana).

Normally?
Undead are Knowledge(Religion), not Arcana, even though they're produced by spells.

What do you do when you get critters that fit more than one category (e.g., Incorporeal Undead)?
Your forgot Elementals (Knowledge(The Planes)), obviously.

[Duke of URL]

In Boundless Horizons, we made an option of the "sneak attack" (renamed precise strike, with sneak attack as an option) ability called exploit weakness, which is a full-round action that combines a Spot check (DC 10 + creature's HD) with an attack roll -- if both are successful, you can apply precise strike damage to anyone normally immune to precision damage (undead, constructs, fortification, etc.), plus you gain stacking insight bonuses to subsequent Spot checks for future exploit weakness attempts against the same creature.

No feat required, it's part of the standard level 1 rogue ability.

[Cicciograna]

While this is an admirable idea, I think you've over-reached. Instead of making the skill check a swift action, I suggest it should require a move action instead. This is consistent with the way Spot and Listen checks, to try to perceive things that aren't apparent initially, work. This change would impose a real tactical cost on the Rogue, whereas a swift action is for most purposes "free". You can always change the time requirement with an additional resource, along the lines of the Quick Reconnoiter feat (grants 1 Listen and 1 Spot check each round as free actions).

While a move action would be more interesting in terms of tactial costs for the Rogue, given that this class is heavily based on movement and position maybe it would be too disadvantageous for them. That's a good suggestion, however.

HD + 10, I suppose, or it would be autosuccess.
Maybe 10 + HD/2 if it scales too fast.

Not a bad idea, inherently, but that's a rather low DC. Standard DC's for recognizing a critter are 10+HD.

Consider that not all the skills involved are class skills for the Rogue. 10+HD could be too much: I like 10+(HD/2), what would you think of 5+HD?

Undead are Knowledge(Religion), not Arcana, even though they're produced by spells.
[...]
Your forgot Elementals (Knowledge(The Planes)), obviously.

Completely missed both. Thank you.

What do you do when you get critters that fit more than one category (e.g., Incorporeal Undead)?

In that case, use any of the skills viable for both the types (in your case Heal, Spot, Knowledge [Arcana or Religion]).

[Person_Man]

The problem with your house rule is that it requires a Skill investment in a bunch of otherwise useless Skills.

I have a standard house rule which any class with Sneak Attack can take. You can trade Sneak Attack for Back Stab. Back Stab functions exactly like Sneak Attack, except that nothing is immune to it, and it only functions when you Flank an enemy. Similarly, nothing is immune to Skirmish, but it only functions for ranged and thrown attacks. Or you can keep the RAW if you prefer, but then you have to deal with immunities.

Honestly, in a world of Leap Attack, there's no reason to nerf Precision Damage. It's just a massive bookkeeping hassle.

[RMS Oceanic]

I think houseruling this would work very well with Knowledge Devotion.

[Otodetu]

The problem with your house rule is that it requires a Skill investment in a bunch of otherwise useless Skills.

I have a standard house rule which any class with Sneak Attack can take. You can trade Sneak Attack for Back Stab. Back Stab functions exactly like Sneak Attack, except that nothing is immune to it, and it only functions when you Flank an enemy. Similarly, nothing is immune to Skirmish, but it only functions for ranged and thrown attacks. Or you can keep the RAW if you prefer, but then you have to deal with immunities.

Honestly, in a world of Leap Attack, there's no reason to nerf Precision Damage. It's just a massive bookkeeping hassle.

I agree, but i simpy added "half sneak attack if it's normally immune".
Works like a charm, and there really is no need to overcomplicated, use that fertile imagination on your champaign; make some npc's or lands.

[ericgrau]

Knowledge checks are typically free actions. Retrying a spot or listen is a move action, but otherwise those are free actions too. 10 + HD is the typical DC. But ya, it does scale faster than rogue levels if you stick with this. The other issue is that many of these skills are cross class for rogues. None of the skills themselves are useless, because they also tell you other weaknesses of the related monsters. But ya it is a lot more skills for the rogue to spend points on.

I'd maybe add craft(alchemy) to oozes. Heal and spot are a bit of a stretch IMO. Incorporeal are usually undead which fall under religion. Those magically incorporeal would fall under spellcraft.