Ninja Penguins are one of the three species introduced in version 1.3.2g.
Ninja penguins spawn at night in most snowy biomes. Unlike most other species of penguins, they spawn like monsters rather than animals, so they will respawn every night.
Ninja Penguins cannot be tamed. They will attack players on sight and they wield two weapons. They will sometimes stand at a distance and throw their shurikens, which deal half a heart of damage. However, if you get too close they will begin leaping at you with their katanas, which have the strength of an iron sword.
On death, Ninja Penguins will drop 0-8 Penguin Shurikens and have a 33% chance of dropping a Penguin Katana. These weapons can then be used by the player. See their respective pages for more information.