During the 2012 "Lost Tribe" promotion, Yellow and his fellow M&M's set a course following his ancestor's directions to find a lost tribe of their kind. On an island, they discover the Lost M&M's Tribe who then proceed to attempt devouring them.
As seen, the Lost M&M's Tribe consists of more primal versions of the five main M&M's and even match them somewhat in terms of personality. A good example of this is seen in the commercial "DNA Test" where a Yellow-resembling tribesman (possibly the leader) begins communicating in his language before unintentionally embedding a spear into his foot. This act is deemed as proof that he and Yellow are related somehow. This also extends to other M&M's such as the Orange parallel demonstrating paranoia and the Green parallel being somewhat flirtatious and coquettish with Blue.
The Lost M&M's Tribe also demonstrates many attributes of stereotypical cannibals. They have sharpened teeth, facial markings, and a habit of licking their prey (playing up on the fact that they are anthropomorphic candies). They also have a cauldron set up to prepare their intended victims. But most dangerous of all, they are relentless in hunting down their intended prey. They are guided by their hunger, even going after those who attempt to hide in the local caves as Red, Yellow, and Orange found out.
In the Promotion
In the first advertisement of the series, Yellow and his associates go through a jungle and come across the settlement of the Lost Tribe. Immediately, the Lost M&M's Tribesfolk tie the M&M's to poles and ready a cauldron to prepare them for supper. Yellow protests that he was not meant to be eaten while Blue and Red insist that he is as an attempt to save themselves. This extends to other adverts, such as Blue and Yellow being dangled over cooking fires and Orange attempting to flee his counterpart that seasons him. In another advert however, the M&M's mistake the bubbling cauldron for a jacuzzi and do not seem to notice the Red analogue cutting up carrot slices into the water.
At some point, the M&M's escape and flee for their lives with the Lost Tribesfolk in hot pursuit. One advert shows Red and Yellow hiding out in a dark cave, only be to caught and licked by the Red analogue when it turns out he was there the whole time. There is also the aforementioned Orange counterpart seasoning his head and later tracking him in another cave. For the most part, the latest adverts in the series have consisted of the cannibalistic M&M's trying to hunt down and kill their known counterparts.
It is implied that they may have killed Yellow's ancestor when he discovered their location. However, given the alleged evidence that at least Yellow is biologically related to the tribe, it is also possible that Yellow's ancestor went native. During the "Escape" videos seen in a later advert, a shrunken head matching Yellow's ancestor's description (notably the mustache), is found by Yellow, suggesting either outcome.