According to myth, it was said that the world would one day be cast into darkness. At that time, the earth would take action to defend itself, and the Five Elements would appear, assuming physical forms to become the guardians of the world. When they arrived, they would seek out those they deemed unworthy, and replace the current protectors with themselves.
And so a group of five warriors, consisting of a tigard ("Earth"), a gorilla ("Metal"), a crocodile ("Water"), a flamingo ("Fire"), and a tarantula ("Wood"), appeared outside of the Jade Palace before Po and the Furious Five. Though they demanded that the Kung Fu masters step aside so they could take their places as the defenders of the Valley, Po and the Five refused, and the panda stood up to "Earth", and called on the others to attack. Not getting the cue, however, the Five were soon overwhelmed and captured along with Po.
Though Po and the Five assured the five warriors that they would not get away with this, they were taken by surprise when brought to the Palace, where Master Shifu welcomed their captors as honored guests. Earth expressed surprise at Shifu's worship of them, the first sign that the quintet were not as they appeared. After smelling a familiar scent from Fire and becoming suspicious, Po told the Five that he had a plan. He used his weight to make the pole that he and the others were tied to come out from the ground, and shifted to hit the five warriors while still tied up.
Soon released from the ropes, Po and Furious Five stood to do battle, declaring that they would never let the warriors enter the Jade Palace. On Earth's command, "Metal" stepped forward, threatening Po with a giant blade, but was received with a kick in the back of the head by Shifu, who cued his students to attack. While they battled, Shifu told them that he knew he couldn't fight the five warriors by himself, so he had kept the enemy close until the Po and the others were free.
Po then told the others that the five warriors were not the real Elements, even though each of them (except for Earth) showed a demonstration of their elemental namesakes. Po had recalled the smell from "Fire": Sesame oil, a very flammable oil used for seasoning. The group of warriors attacked in response, and the battle resumed. Being the largest of the elements, Metal was difficult to defeat, but was eventually brought down after battling several of the kung fu warriors.
After all his comrades had been defeated, Earth finally revealed that they had meant to deceive them so that they would be allowed into the Jade Palace in order to steal its priceless treasures, before Mantis promptly incapacitated him. With the imposters tied up, Po and the Five uncovered how the group had made their "powers" using sesame oil and hidden containers. Po explained how Metal would use his sword to create a spark to ignite the sesame oil Fire carried in order to produce his flames, the reason why the two were always together whenever Fire used his 'power'.
Little is known about Metal's personality, other than he is as conniving and brutal as his comrades.