Disguise/Alter Self and Disguise checks

[Chronos]

This is a dispute from the Simple Q&A thread:


Q 217

Do magical bonuses to disguise, such as from Alter Self (http://www.d20srd.org/srd/spells/alterSelf.htm) and Disguise Self (http://www.d20srd.org/srd/spells/disguiseSelf.htm), stack?

Q 217 clarification

Fixed the initial question
Per the general rules here (http://www.d20srd.org/srd/theBasics.htm#modifierTypes), I suggested that they do indeed stack. Also, the relevant spells are Disguise Self and Disguise Undead. This adds an additional layer of differentiation between the spells providing the bonus, since one isn't directly derived from the other (disguise & alter self)

I maintain that they do not stack, or at least, if they do, they don't behave the way they appear to. First, the relevant quotes from the SRD: From Disguise Self (http://www.d20srd.org/srd/spells/disguiseSelf.htm):

If you use this spell to create a disguise, you get a +10 bonus on the Disguise check.
We'll call this Bonus A.

Similarly, Alter Self (http://www.d20srd.org/srd/spells/alterSelf.htm):

If you use this spell to create a disguise, you get a +10 bonus on your Disguise check.
Call this Bonus B.

But also, from the Disguise skill description (http://www.d20srd.org/srd/skills/disguise.htm):

Magic that alters your form, such as alter self, disguise self, polymorph, or shapechange, grants you a +10 bonus on Disguise checks (see the individual spell descriptions).
Call this Bonus C.

Now, are these the same bonus, or different bonuses? If Bonus C is the same bonus as Bonus A, and also the same bonus as Bonus B, then it follows that Bonus A and Bonus B are the same bonus, and so do not stack. This is what I claim happens. Some, however, claim that Bonus A and Bonus B are separate bonuses, and do stack. But if this is the case, then Bonus C must also be a separate bonus, and would also stack: Thus, Disguise Self by itself would give a total of +20 to Disguise, and using both spells together would give a +30. Since I don't think this is what's intended, I hold the former interpretation.

[prufock]

Both A and B are contained in the set C (even mentioned by name), so C includes both, thus C+A and C+B wouldn't stack. A+B is murkier. As unnamed bonuses, one would expect them to stack, and RAW I believe they would. However it seems as though "magic that alters your appearance" (set of C), is intended as the source, and bonuses from the same source don't stack.

So...
RAW yes, RAI probably no.

[Segev]

I think you're correct: the two spells are re-stating the general rule, not introducing a new bonus on top of it.

[broodax]

Further argument that they do not stack: It is only if Alter Self is used to "create a disguise" that it grants a bonus. If you use Alter Self to create your disguise, you cannot also use Disguise Self to create the same disguise, the disguise already exists.

You could create a new disguise, but this would simply result in a new, separate check, not a bonus to your previous check.

[Cruiser1]

If you use Alter Self to create your disguise, you cannot also use Disguise Self to create the same disguise, the disguise already exists.
Indeed. Note that Polymorph effects replace each other. If I Shapechange into Alex, then Polymorph into Bob, then Alter Self into Carl, and finally Disguise Self into Don, I look like Don. I don't look like Alex, Bob, or Carl. Therefore there's only one disguise, and only one Disguise check bonus.

However, note that the above only concerns visual effects (i.e. Disguise skill check opposed by Spot skill check). Some spell combinations may give circumstance bonuses to creating disguises that don't rely on vision. Disguise Self only changes your appearance, and may be overcome by a will save. Alter Self actually changes your form through transmutation, so you can shake hands and such without them interacting with an illusion. Alter Self into someone, plus Disguise Self so you have their typical clothing, allows you to shake hands and such without people getting will saves (unless they touch your clothing). Add Shapechange into some creature with (Su) abilities similar to their spellcasting, before Alter Self for form, and Disguise Self for clothes, and your overall disguise is even better. However your visual Disguise skill check opposed by Spot skill checks still isn't changed or improved any.

[Sith_Happens]

Further argument that they do not stack: It is only if Alter Self is used to "create a disguise" that it grants a bonus. If you use Alter Self to create your disguise, you cannot also use Disguise Self to create the same disguise, the disguise already exists.

You could use each to create different parts of the disguise. For instance, Disguise Self can change your clothes and Alter Self can't.