Disguise to different Creature Type

[Echoen]

Here's the situation: I'm the DM for the Pathfinder module Wrath of the Righteous. We're in Book 4, which states:

"Note that if the PCs aren't disguised as demons, all
encounter rolls on the following table should be modified
by +40, Alushinyrra's danger rating."

"If the PCs...disguised themselves as bodaks and graveknight...."

Here's the problem: There is no way that we've found that permits a creature to use Disguise to alter its type. Humanoids cannot disguise as Outsiders or Undead.

Is there something we're all missing?

http://www.d20pfsrd.com/skills/disguise

[Claxon]

If nothing else, polymoprh spells should allow you to be disguised as appropriate creatures. But you are correct that the disguise skill itself does not grant you the ability to disguise yourself as another type of creature.

[Milo v3]

Disguising yourself as a different race is not limited to races of the same creature type as you. You can disguise yourself as a demon/bodak/graveknight.

[Diego Rossi]

PRD - Disguise skill wrote:

Disguised as different race

It don't say "a different race of yours type".

I would add modifiers, but nothing say that you can't try to disguise yourself as something that isn't of your type.

[wraithstrike]

Does the disguise skill specifically limit you to creatures of your type?

I mean somethings are obviously not going to work, such as a human looking like a cat, but I see no reason a human can't look like a teifling or succubus since both have a humanoid shape.