It was briefly mentioned in the episode 'The Kung Fu Kid' that Peng is from 'the valley over' from the Valley of Peace, where he was presumably raised by his family and learned pottery. It is unknown, however, when Peng started training in Kung Fu, though he admitted at one point to have no formal training, hinting that he is self-taught.
When he became a teenager, Peng left his hometown in search of his Tai-Lung, though it is unknown how much he knows of his uncle. He stopped in the Valley of Peace to partake in the Peace Jubilee, where he would be discovered as a Kung Fu prodigy by the master of the Jade Palace.
In Legends of Awesomeness
Peng made his debut in 'The Kung Fu Kid'. Upon arriving in the Valley of Peace to partake in the Peace Jubilee, someone proposed that Peng fight Jing Mei, the nephew of Temutai, who was one of the masters hosting the celebration. Peng was hesitant until Jing Mei knocked down his pottery cart, and agreed to the fight. He introduced himself to Master Shifu and assured the Dragon Warrior that he wanted to fight. When the match began, Peng first evaded Jing Mei's attacks but then countered one and finished the fight with three airborne spin-kicks, easily winning the match. Before he could take his leave, both Po and Temutai tried to convince Peng to train with one of them, almost turning into a fight until Shifu declared it was Peng's choice. The young snow leopard decided to train with Po at the Jade Palace.
On their way to the Palace, Peng was mobbed by a group of children who had become his new fans and signed autographs before at last he was taken to the Training Hall where he met and was complimented by the Furious Five, who offered him a run through the training course. Peng traversed it in seconds flat. At dinner, Peng sat at the head of the table (where Po was supposed to be sitting as host) and told some jokes, succeeding in making Tigress laugh.
Later, he met up with Po in the Training Hall again, where the Dragon Warrior haltingly told Peng that Shifu had dismissed the young potter's skills as a warrior. This outraged Peng, who declared he'd prove Shifu wrong before running off. He sought out Temutai and told him what happened before picking up a sword, proclaiming he would defeat the Qidan Clan leader and show Shifu what 'real' strength is.
During their fight, Peng got Temutai on the defensive when they were interrupted by Jing Mei. Not wanting to get involved he quickly excused himself, much to his uncle's fury. Finally, Po showed up and tried to stop the fight; but Peng refused to back down, exclaiming he 'practiced his Kung Fu without any plans, no expectations, and no dreams' until Po 'gave him one' and Shifu 'snatched it away'.
The fight continued outside and before long, everyone (the Furious Five, the Qidan Warriors, and the villagers) were all fighting and squabbling until Po shouted for everyone to stop. Here, Peng got a confession from Po that he was the one who wanted Peng gone, not Shifu, because he got jealous of Peng's popularity, and sincerely apologized. Though shaken, Peng found it in his heart to forgive Po, and partook in the closing ceremony with Po and Temutai by performing tai chi.
When the Jubilee was over, Po invited Peng back to the Jade Palace, but Peng politely declined as he wanted to continue his travels, revealing that he was searching for his uncle. When Po asked who his uncle was, he received a shock when the young snow leopard revealed that his uncle is Tai Lung.
Peng later made another appearance in 'Master and the Panda'. He returned to speak to Po after finding out about his uncle. When Po reveals the truth Peng is angry and tries to attack Po, believing that Tai Lung wasn't evil. However Peng returns to the Jade Palace and realizes Po was right about everything and that Kung Fu causes evil. Peng quits Kung Fu and leaves behind his uncle's sword.
When Temutai attacks the Jade Palace wearing a the Gong Lu Medallion, Po seeks out Peng's help and convinces him that he won't turn out evil. They defeat Temutai as a team and knock the medallion off him. However Peng picks up the medallion and the power corrupts him. He starts to attack the Five and then Po, causing them to roll down the stairs (similar to the fight in the first movie).
Peng knocks Po aside wishing his uncle was still around to see his victory. Tai Lung appears from the shadows, stating he is a manifestation from the medallion. Tai Lung instructs Peng to destroy everything including the innocent, however before Tai Lung can hurt anyone Peng stops him, stating that he is nothing like Tai Lung and takes the medallion off himself. Tai Lung then transforms back into Po (who used a shift stone to change his appearance). Po tells Peng that despite having a dark side he was able to stop before he went to far. However, Peng still believes that he holds some of the same evil that corrupted Tai Lung and leaves the Jade Palace, vowing to never do Kung Fu again.
Peng appears again in the episode 'Kung Fu Club', where he and another snow leopard named Lian, who is also his girlfriend, open up a Kung Fu fight club despite it being outlawed. He first appeared as a masked figure in the episode, and when fighting Po, who was attempting to shut down the fight club by orders of Shifu, he takes off his masks and reveals himself, knocking out Po.
When Po wakes up, Peng and Lian explain that after he quit doing Kung Fu, he and Lian opened the fight club because they believed that Kung Fu masters can't be everywhere, so they decided to teach people Kung Fu so they can defend themselves from criminals. So Po, agreeing with Peng's words, joins the club behind Shifu's back. Eventually, people in the Valley of Peace are capable of hording off bandits.
Eventually, Tong Fo appears and kidnaps Lian, and uses her to bribe Peng into killing Po with a poison-needle. When the bandits take over the fight club, Peng battles Po, and secretly reveals Tong Fo's involvement, and manages to fool Tong into thinking he succeeded in killing him. When they least expect it, Po and Peng fight off the bandits, and when Tong was prepared to kill Lian, he suddenly realizes that Lian had already escaped. After the battle, Shifu appears after seeing everything in disguise. After being awestruck by the fights, he decides to lift the ban of fight clubs. Afterward, Lian and Peng decide to open up more fight clubs across China.
Role in the series
Peng was previously going to appear in a Season 2 episode until a misunderstanding between Scroopfan and Tman lead to the episode being canned. Yet he soon appears in Equestrian Kung Fu Fight Club where he and Lian decide to open up a fight club in Equestria.