I am developing a series of dolls, and want to make sure I won't become subject to copyright infringment law suits.
Intellectual Property Law Attorney
You've already received responses to a very similar question. http://bit.ly/F6ski
A doll cannot parody anything. The Supreme Court defines a parody as a literary or artistic work that imitates the characteristic style of an author or a work for comic effect or ridicule or as a composition in prose or verse in which the characteristic turns of thought and phrase of an author or class of authors are imitated in such a way as to make them appear ridiculous. Dolls can't do that and so parody is no defense to a claim that your dolls infringe someone else's copyright.
If your business model is to create and sell dolls that are based on the works of others then you need to speak to an intellectual property attorney.
Since parody is a version of the fair use defense to a claim of copyright infringement, this question starts from the premise that what you plan to do may expose your doll creations to such a claim. You can't assume that you can ever be sure that any proposed work won't get you sued - this isn't an area of law that's got bright line rules, it always depends on the specific original work and the alleged infringing work.
I think it's difficult but not impossible for a doll to parody an original doll, and I don't think any court has ruled that parody is necessarily limited to only certain kinds of copyrighted works.
But dolls seem to offer less opportunity to mock or comment on some other dolls, as compared to the ability to poke fun at novels and songs. You should consult with an IP lawyer before you launch your line of parody dolls so they can see exactly what you have in mind.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.