I dunno', what if it was one boss zombie, or like... uh is it Night of the Living Dead? Where individual zombie parts come back to life, to the point where burning them just spreads zombiejunk all over.
One zombie of the right type could be a death sentence for the whole planet!
The criteria is that it's a horror villain of your choice. So, I don't know why you'd choose a boss zombie or one of those really bad variants when you could choose one of the zombies from Shawn of the Dead.
But I'm also not completely sure that a random zombie really counts as a "villain".