Is a shadowdancer's shadow companion supposed to have the HD of its master (for the purposes of things that can effect it) kind of like a familiar does? It seems weird to be 15th-level with a 100+ hp shadow that only has 3 HD.
Sorry to commit Thread Necromancy, but Jeff Clem's answer here is just so wrong that it requires refutation for those reading later.
The Shadowdancer rules say: "This shadow has a number of hit points equal to half the shadowdancer's total. The shadow uses the shadowdancer's base attack bonus and base save bonuses."
Clearly, like an arcane bond's familiar, the shadow companion uses his master's full BAB and saves and half his full hit points, not just those deriving from the prestige class.
Is it evil to use a thread that has already been necromanced?
I understand why Jeff is saying that:
Character Level: The total level of the character, which is the sum of all class levels held by that character.
Class Level: The level of a character in a particular class. For a character with levels in only one class, class level and character level are the same.
So it could be read that the Shadow only gets half of the Hit Points from the Shadowdancer class, if it was intended to have half the characters HP, it should say "half the character's total". I doubt this is the intent.
They use the same "shadowdancer's" wording with the spell like abilities, with the intent (assumed) being there that the Caster Level for those abilities is the shadowdancer level, not the character level.
A very similar question comes up when using Eldritch Heritage for and arcane familiar. Does that familiar have reduced HP, saves, and HD?
It say's half of the shadowdancer's total, which seems pretty clear to me. If the shadowdancer has 100 hp, the shadow has 50. Just like a familiar.
Ravingdork's original question, which was never answered, was how many HD, not HP, the shadow should be considered to have, for things like being effected by spells (i.e. a spell that effects things of 4HD or less.) Familiars have a specific rule that has them considered as having the character's HD for this sort of thing, but that line is not present in the shadowdancer PRC.
As the rules stand (unless there is a FAQ I'm not aware of), the shadow has 3 HD. I expect if Paizo were to clarify this they would change that. It is a reasonable house rule to have the shadow be considered to have the shadowdancer's HD for such purposes, like a familiar.