Change Shape cap HD?

Question

Simple question. A succubus, an ogre mage, or any other creature with the Change Shape supernatural ability can take the form of an humanoid (Or even Giant for the Ogre mage)... It does not specify this ability works like a polymorph effect. It is not Alter Self either... It is almost like Alternate form but even less good. The wild shape ability from a Druid or any other class granting this feature specifically calls a limit of Hit Dice you can transform into. But not for Change Shape.

And I can't find any answer anywhere.

So. Is there a rule saying, as for Wildshape or Polymorph, the Change Shape ability has capped hit dice OR does that mean you can take any form you want, no matter the HD of the creature? (Since you only get some ex, no hit points, no natural armor etc... This limitation does not seem significant... Except if you are using Assume Supernatural Ability. Which I do not plane to use. And is not why I ask this question. Not at all.)

Answer 1

Change shape is almost entirely cosmetic,

A creature with this special quality has the ability to assume the appearance of a specific creature or type of creature (usually a humanoid), but retains most of its own physical qualities.

^{(Change Shape special ability description)}

so an HD cap would be somewhat odd. Indeed, the only things that actually change beyond your appearance are

• […] It gains the size of its new form.

• The creature loses the natural weapons and movement modes of its original form, as well as any extraordinary special attacks of its original form not derived from class levels (such as the barbarian’s rage class feature).

• The creature gains the natural weapons, movement modes, and extraordinary special attacks of its new form.

^(ibid.)

Everything else in the description is about how things don’t change. Combine that with the fact that change shape is find (near?) exclusively on monsters, not player-focused material,¹ and is a supernatural ability, so players cannot easily access it by via their own polymorph effects,² and there just wasn’t a lot of reason to limit it.

So yes, an ogre mage can look like as powerful a giant as they can think of, as long as it isn’t too big. It won’t have much of what made that giant so powerful, though.

1. _{Yes, technically, an ogre mage or succubus is legal as a player character so long as you’re playing at a high enough level. But the entire point of the Level Adjustment system is to account for powers that may be more dangerous in player hands than DM hands. And in practice, it goes much too far, basically crippling characters with LA—the ogre mage and succubus aren’t really playable.}

2. _{It’s a consistent thing that most forms of polymorph don’t allow you to gain the supernatural effects of the new form—that feature was originally limited to the 9th-level shapechange spell. Of course, they later printed Assume Supernatural Ability and Metamorphic Transfer, which make it much, much easier, but those wouldn’t have been assumed at the time change shape was written up—and those are widely regarded as mistakes anyway.}