When a guest donates to a killer penguin exhibit, instead of the standard "I gave the zoo a donation" thought, the guest thinks "I wonder if I give the penguin money, will it be nice to me?" Despite tundra being the proper biome, a game announcement may say that the killer penguin is in the wrong biome.
In Zoo Tycoon 2
The killer penguin is a reference to a glitch in the first Zoo Tycoon game, in which emperor penguins were able to kill animals they shouldn't have been able to kill, such as zebras. However, the Killer Penguin more closely resembles a giant Rockhopper Penguin than an Emperor Penguin. It is possibly a reference to the penguins from the Madagascar films, considering the Zoopedia states that it is from Madagascar. Sometimes, a killer penguin will replace the scientist in the extinct creatures creation minigame. According to the killer penguin's Zoopedia article, if someone offers you a penguin for free, you should say no. Sometimes in challenge mode, somebody will indeed offer you a free penguin, which is actually a killer penguin and should never be adopted. Killer penguins cannot be put up for adoption (most likely because nobody in their right mind would dare have it in a zoo) or released into the wild (unless they are very, very happy). The only other way to get rid of it is for it to die somehow (die of illness, die of old age, get killed by another predator, etc.) If you do not want the killer penguin in your zoo, but you got it anyway from a mistake in the extinct research lab, you can (and should) recycle it.
Because you can get other mistake animals from the extinct research lab, such as squirrels or butterflies, their crates can be recycled. According to the Zoopedia, killer penguins "enjoy sunsets, long walks on the beach, and pecking things to death."
The Killer Penguin's happiness increases as it hunts live animals. As an alternative to hunting, Ice Blocks can be given to the penguins. However, if they are capable of hunting, this will take care of enrichment needs, rendering them unnecessary and troubling to have around.
There is a hack at Zoo Tycoon Volcano which makes killer penguins adoptable. However, the hack contains a glitch that makes killer penguins swim on land.
Also if you create a squirrel through a similiar lab failure, and place it in the Killer Penguin's exhibit, the penguin's status shows "Running from Squirrel", which is strange, considering that it has the ability to kill virtually any other animal in the game, even the dinosaurs, and yet it runs from a squirrel.
There is an adoptable killer penguin by Thomvonder, which can be found at zootycoon.nl.
Based on one player's observations, they seem unable to eat from aquatic fish and meat sources, complaining of hunger even when surrounded by "Lure Bouy with Fish" which is listed in its zookeeper recommendations. While it can kill any other animal in the game, and very much enjoys hunting down land-based and amphibious animals such as emperor penguins and caribou for sport, it seems to leave purely aquatic animals such as orcas and belugas alone unless otherwise provoked. Zoo guests enjoy watching killer penguins and will comment on them, but will not donate for them.