publicity rights). Because Night of the Living Dead is public domain, there is no copyright owner from whom you'll need permission. However, you would need permission from the actors and it appears as if Sphereworx, (the company that has registered the trademark) has already acquired permission from the four actors used in their initial action figure release. So, besides the trademark issues (discussed below), you already face some major obstacles getting consent from the actors.
Using trademarks to protect public domain works. 100 years ago, the Supreme Court held that the title of a public domain book -- Webster's Dictionary -- also fell into the public domain and could not be protected by trademark law. The Ninth Circuit reaffirmed this rule in a case involving the John Wayne movie, McLintock. However, these cases involve someone claiming trademark rights in a book title for a competing book and a movie title for a competing movie. The rules are different if a public domain movie title is used for non-movie goods or services -- for example, It's a Wonderful Life is a registered trademark for lottery services. We can't predict the outcome of a case in which a public domain movie title is used to prohibit others from selling character merchandise ... but we doubt you want to pay to find out.
P.S. Speaking of salvaging from the PD, even Night of the Living Dead spawned a copyrightable slogan, "When there is no room in hell … the dead will walk the earth” (Dawn Associates v. Links, 203 U.S.P.Q. 831 (N.D. Ill. 1978)