House Cat

In Dungeons & Dragons normal animals are given stats like monsters. These generally fall into three types. 1: Herbivores used as beasts of burden 2: Carnivores that are meaningful fights through wilderness ambush, gladiator fights or guard animals 3: domestic animals and normal birds for use as a Familiar or something a Druid can morph into/befriend. Among the third type is normal, domestic cats.

In 3rd Edition Dungeons and Dragons, house cats actually belong to the second category. They have stats that make them incredibly deadly combatants for their apparent harmlessness and low Challenge Rating. Thanks to a tiny size and high dexterity, a cat has an armor class that makes it as hard to hit as a man in a chain shirt. The cat is actually harder to hit since that AC is all touch AC, so splash weapons and energy rays will not save you. They are also very stealthy and win initiative, so they can ambush easily. A cat has three natural attacks, all doing 1 damage each. Statistically a cat will virtually always kill a level one Commoner one on one. If a level one Wizard that doesn't have a familiar helping fight back is very likely could die as well. Even if he can get casting off (which is already a resource expenditure far in excess of its supposed CR), few first level Wizard spells are that likely to work on the monster thanks to low damage that is likely halved (and if it's a familiar attacking you, outright avoided) by the cat's high reflex save. More meaty classes fare better, but still need disproportionate effort to kill it.

Pathfinder nerfs them slightly, but only through a minor, easily overlooked system wide change: Damage reduced to less than one by damage penalties does one non-lethal damage. In 3E this was still lethal damage. Now a victim has a chance of being rescued after being KOed but before the cat finishes them off. This does raise the question of how cats can actually kill rats without first KOing them.

Not to be outdone by the other Wizards of the Coast game, Magic: The Gathering also got in on the action. Sanctuary Cat debuted in Innistrad. It normally wouldn't be a notable card, it's a 1/2 white one drop and a functional reprint of one of the oldest cards in the game with a generally worse type and a few strictly better cards have been printed. This card became notable because the art depicts what seems to be a normal cat. Since 1/1 has always been the normal power and toughness for one mana creatures, this cat can kill a surprising number of things and live. Most of these creatures were still trained and armed/armored soldiers.

Monstergirls

See Catgirl.