In Japanese folklore, the tanuki is one of the most well known of all yokai. They are believed to have magical and shape-shifting powers and many folktales tell of unsuspecting people being tricked by a tanuki. This yokai is the supernatural form of the real animal tanuki, sometimes referred to as 'racoon-dog' in the west. While once viewed as evil tricksters, today in Japan, you will see that statues of tanuki are often placed outside shops and restaurants to bring good fortune and success.

One of the tanuki’s most peculiar and distinguishing features are their extremely large and expandable scrotums. They can change form and be used for such things as temporary shelters, fishing nets, weapons, boats and even parachutes, as famously depicted in the Studio Ghibli film Pom Poko. It seems the tanuki's giant testicles are symbolic of stretching wealth and prosperity, which is why they are used as a way of attracting good luck.

Tanuki and their 'parachutes' in Pom Poko - Studio Ghibli

In the Edo period, ukiyo-e artist Utagawa Kuniyoshi created a series of prints depicting tanuki and their special talent for making good use of their magical expanding scrotums. This first series of four prints below show them used for fishing and hunting.

In the next four prints the tanuki use their special gift for weightlifting practice, killing a catfish, keeping warm and as a boat. Because...well, why not?

And here we have some more random tanuki craziness. There is some serious expansion happening in the third print below. 
In the second print below the tanuki even use their expanding scrotums to disguise themselves as tengu (another yokai with a long nose).

Throughout yokai folklore, it is often suggested that if no explanation can be found for mysterious supernatural phenomena, it could simply be the work of a tanuki in disguise. 

'Tanuki' - Tsukioka Yoshitoshi, 1881.

Tanuki statue on Enoshima

'Pom Poko' - Studio Ghibli