Pirate/Zombie/Ninja is the 21st Century's Rock/Paper/Scissors

Lev Grossman has declared that zombies are the new vampires.

This may be true in its own way, but it ignores a more pressing concern: What mythological forces can defeat each other? And can they be assembled into some sort of rock/paper/scissors system? The answer, after laborious research, is definitive.

Pirates can defeat zombies, as is well known. 

Equally, zombies can defeat ninjas; barring a few a few spurious oral histories , there is no reason to believe that ninjas can successfully defeat zombies. Zombies cannot be fooled by illusions or smoke bombs, and their limbs and nerves cannot respond to the powerful secret arts of the ninja. Though the ninjas may fight valiantly, they will be ultimately overrun. 

This leaves us, of course, with the crux of the debate: pirates versus ninjas. While some accounts indicate that pirates would be superior, think carefully about any potential engagement. The pirates would be drunk with grog, while the ninjas possess clothes as black as the sea, swords as sharp as a northern breeze, and blows as powerful as a hurricane's gale. At land, the pirates lack ship-based firepower, and Lone Wolf and Cub establishes that ninjas are equally at comfortable at sea as at land. While pirates use their cannon to win a decisive advantage over the slow-moving and easily-friable zombie, those advantages fall away when faced with stealthy and swift ninja operatives. Any serious contemplation of the issue leads one to believe that the ninjas would destroy the pirates.

There one has it: the pirate/zombie/ninja circle. Pirates beat zombies, zombies beat ninjas, ninjas beat pirates. Tell your friends.