Hundun has two eyes on each side of it's head, along with two backwards facing prongs that appear like shovels, one on each side of the head. It has a crest on top of it's head too.
Six months after Trespasser attacks San Francisco, Hundun emerges from the Breach. The Kaiju makes landfall in the Philippines; specifically at Taal, in the Batangas province, at night during a tropical storm. It crosses Taal lake, then crosses Laguna de Bay, approaches Metropolitan Manila and attacks Manila itself.
By the time officials know what is happening, Hundun is rampaging through the city, causing widespread death and destruction and terrorizing the inhabitants, before being finally killed by a tactical nuclear strike.  However, though it is killed, its excrement severely contaminates the environment of the city.
Because the attack occurred prior to the formation of the Pan Pacific Defense Corps, Hundun does not have a category.
- Hundun is the name of a character in Chinese mythology, and the "primordial chaos" of Chinese cosmogony.
- Hundun's entire head appears in Mirada Studio's featurette "Pacific Rim 'Before and Afters" (see: video below).