Strong cartoon violence throughout. Penguins are beaten, strapped, 'shot' (with snowballs), impaled and crushed, all with bloody results.
Cannibalism is a plot point in the first few episodes. A penguin is shown chopped up in a furnace. Another barely-alive penguin is dragged by a cannibal (presumably to be eaten), with a large blood trail left behind.
A female penguin is set on fire. The voice acting gets surprisingly disturbing as she screams in agony and her voice distorts. Her arm then falls off as she dies.
In silhouette, a penguins corpse is gutted via its mouth. Organs, intestines and eventually it's entire skeleton can be seen being removed. While in shadow, this is arguably the vilest moment in the show.