The pygmy hog is the smallest pig species in the world — standing just 25 centimetres (9.8 in) at the shoulder. It is also one of the rarest. Once widespread across the southern foothills of the Himalayas, fewer than 250 mature individuals now survive, confined to a small patch of grassland in Assam, India. 

The saola — often called the "Asian unicorn" — is endemic to the Annamite Mountains of Laos and Vietnam. Discovered by science in 1992, it has never been directly observed alive by researchers in the wild and may number fewer than 100 individuals.

The Bawean hog deer is the rarest deer in the world. It's only found on the small Indonesian island of Bawean and is considered 'critically endangered' — with an estimated population of fewer than 300 individuals.

The Chacoan peccary was initially described as an extinct species from fossils discovered in 1930. In the early 1970s, a living population was found in an isolated area of Paraguay — in a region known as the Gran Chaco. This species is the largest and rarest of the three living peccaries.

Often described as ghostly, the elusive Japanese serow lives in the wooded mountains of central and southern Japan. Typically solitary, it stands on rocky outcrops, staring down at the landscape for extended periods — likely watching for predators or rivals. It can be active both day and night.

A male Visayan warty pig can become four times larger than a female. During mating season, the male uses his tusks for combat and three pairs of warty growths on his face for defence — he also grows a 23 cm (9 in) long mane to attract females. The species is only found on two Philippine islands.