According to the Youtube description:» Call of Duty Nazi Zombies comes to life at The University of North Carolina at Greensboro, when two UNCG baseball players discover they are transported into a baseball zombies version of the COD game. (diehardsport.com)
If you manage to clear the area and rescue all the POWs, you'll unlock zombie version of some of the Metal Slug heroes. (toucharcade.com)
Speaking of, the bosses are a reasonably colourful and imaginative bunch the include zombie versions of Kill Bill villains, an insect like dragon, and a bizarre centaur / genie hybrid of sorts. (nonfictiongaming.com)